refactor(forge): extract ForgeBackend class and registry (#129)

* docs: document S3 backend, auto-auth, and `:Pending done` command

Problem: The S3 backend had no `:Pending s3` entry in the COMMANDS
section, `:Pending auth` only mentioned Google, the `sync` config
field omitted `s3`, `_s3_sync_id` was missing from the data format
section, `:Pending done` was implemented but undocumented, and the
README lacked a features overview.

Solution: Add `:Pending s3` and `:Pending done` command docs, rewrite
`:Pending auth` to cover all backends and sub-actions, update config
and data format references, add `aws` CLI to requirements, and add a
Features section to `README.md`.

* feat(forge): add forge link parser and metadata fetcher

Problem: no way to associate tasks with GitHub, GitLab, or Codeberg
issues/PRs, or to track their remote state.

Solution: add `forge.lua` with shorthand (`gh:user/repo#42`) and full
URL parsing, async metadata fetching via `curl`, label formatting,
conceal pattern generation, token resolution, and `refresh()` for
state pull (closed/merged -> done).

* feat(config): add forge config defaults and `%l` eol specifier

Problem: no configuration surface for forge link rendering, icons,
issue format, or self-hosted instances.

Solution: add `pending.ForgeConfig` class with per-forge `token`,
`icon`, `issue_format`, and `instances` fields. Add `%l` to the
default `eol_format` so forge labels render in virtual text.

* feat(parse): extract forge refs from task body

Problem: `parse.body()` had no awareness of forge link tokens, so
`gh:user/repo#42` stayed in the description instead of metadata.

Solution: add `forge_ref` field to `pending.Metadata` and extend the
right-to-left token loop in `body()` to call `forge.parse_ref()` as
the final fallback before breaking.

* feat(diff): persist forge refs in store on write

Problem: forge refs parsed from buffer lines were discarded during
diff reconciliation and never stored in the JSON.

Solution: thread `forge_ref` through `parse_buffer` entries into
`diff.apply`, storing it in `task._extra._forge_ref` for both new
and existing tasks.

* feat(views): pass forge ref and cache to line metadata

Problem: `LineMeta` had no forge fields, so `buffer.lua` could not
render forge labels or apply forge-specific highlights.

Solution: add `forge_ref` and `forge_cache` fields to `LineMeta`,
populated from `task._extra` in both `category_view` and
`priority_view`.

* feat(buffer): render forge links as concealed text with eol virt text

Problem: forge tokens were visible as raw text with no virtual text
labels, and the eol separator logic collapsed all gaps when
non-adjacent specifiers were absent.

Solution: add forge conceal syntax patterns in `setup_syntax()`, add
`PendingForge`/`PendingForgeClosed` highlight groups, handle the
`%l` specifier in `build_eol_virt()`, fix separator collapsing to
buffer one separator between present segments, and change
`concealcursor` to `nc` (reveal in visual and insert mode).

* feat(complete): add forge shorthand omnifunc completions

Problem: no completion support for `gh:`, `gl:`, or `cb:` tokens,
requiring users to type owner/repo from memory.

Solution: extend `omnifunc` to detect `gh:`/`gl:`/`cb:` prefixes and
complete with `owner/repo#` candidates from existing forge refs in
the store.

* feat: trigger forge refresh on buffer open

Problem: forge metadata was never fetched, so virt text highlights
could not reflect remote issue/PR state.

Solution: call `forge.refresh()` in `M.open()` so metadata is
fetched once per `:Pending` invocation rather than on every render.

* test(forge): add forge parsing spec

Problem: no test coverage for forge link shorthand parsing, URL
parsing, label formatting, or API URL generation.

Solution: add `spec/forge_spec.lua` covering `_parse_shorthand`,
`parse_ref` for all three forges, full URL parsing including nested
GitLab groups, `format_label`, and `_api_url`.

* docs: document forge links feature

Problem: no user-facing documentation for forge link syntax,
configuration, or behavior.

Solution: add forge links section to `README.md` and `pending.txt`
covering shorthand/URL syntax, config options, virtual text
rendering, state pull, and auth resolution.

* feat(forge): add `find_refs()` inline token scanner

Problem: forge tokens were extracted by `parse.body()` which stripped
them from the description, making editing awkward and multi-ref lines
impossible.

Solution: add `find_refs(text)` that scans a string for all forge
tokens by whitespace tokenization, returning byte offsets and parsed
refs without modifying the input. Remove unused `conceal_patterns()`.

* refactor: move forge ref detection from `parse.body()` to `diff`

Problem: `parse.body()` stripped forge tokens from the description,
losing the raw text. This made inline overlay rendering impossible
since the token no longer existed in the buffer.

Solution: remove the `forge.parse_ref()` branch from `parse.body()`
and call `forge.find_refs()` in `diff.parse_buffer()` instead. The
description now retains forge tokens verbatim; `_extra._forge_ref`
is still populated from the first matched ref.

* feat(buffer): render forge links as inline conceal overlays

Problem: forge tokens were stripped from the buffer and shown as EOL
virtual text via `%l`. The token disappeared from the editable line,
and multi-ref tasks broke.

Solution: compute `forge_spans` in `views.lua` with byte offsets for
each forge token in the rendered line. In `apply_inline_row()`, place
extmarks with `conceal=''` and `virt_text_pos='inline'` to visually
replace each raw token with its formatted label. Clear stale
`forge_spans` on dirty rows to prevent `end_col` out-of-range errors
after edits like `dd`.

* fix(config): remove `%l` from default `eol_format`

Problem: forge links are now rendered inline, making the `%l` EOL
specifier redundant in the default format.

Solution: change default `eol_format` from `'%l  %c  %r  %d'` to
`'%c  %r  %d'`. The `%l` specifier remains functional for users who
explicitly set it.

* test(forge): update specs for inline forge refs

Problem: existing tests asserted that `parse.body()` stripped forge
tokens from the description and populated `meta.forge_ref`. The
`conceal_patterns` test referenced a removed function.

Solution: update `parse.body` integration tests to assert tokens stay
in the description. Add `find_refs()` tests covering single/multiple
refs, URLs, byte offsets, and empty cases. Remove `conceal_patterns`
test. Update diff tests to assert description includes the token.

* docs: update forge links for inline overlay rendering

Problem: documentation described forge tokens as stripped from the
description and rendered via EOL `%l` specifier by default.

Solution: update forge links section to describe inline conceal
overlay rendering. Update default `eol_format` reference. Change
`issue_format` field description from "EOL label" to "inline overlay
label".

* ci: format

* refactor(forge): remove `%l` eol specifier, add `auto_close` config, fix icons

Problem: `%l` was dead code after inline overlays replaced EOL
rendering. Auto-close was always on with no opt-out. Forge icon
defaults were empty strings.

Solution: remove `%l` from the eol format parser and renderer. Add
`forge.auto_close` (default `false`) to gate state-pull. Set nerd
font icons: `` (GitHub), `` (GitLab), `` (Codeberg). Keep
conceal active in insert mode via `concealcursor = 'nic'`.

* fix(config): set correct nerd font icons for forge defaults

* refactor(forge): replace curl/token auth with CLI-native API calls

Problem: Forge metadata fetching required manual token management —
config fields, CLI token extraction, and curl with auth headers. Each
forge had a different auth path, and Codeberg had no CLI support at all.

Solution: Delete `get_token()` and `_api_url()`, replace with
`_api_args()` that builds `gh api`, `glab api`, or `tea api` arg
arrays. The CLIs handle auth internally. Add `warn_missing_cli` config
(default true) that warns once per forge per session on failure. Add
forge CLI checks to `:checkhealth`. Remove `token` from config/docs.

* refactor(forge): extract ForgeBackend class and registry

Problem: adding a new forge required touching 5 lookup tables
(`FORGE_HOSTS`, `FORGE_CLI`, `FORGE_AUTH_CMD`, `SHORTHAND_PREFIX`,
`_warned_forges`) and every branching site in `_api_args`,
`fetch_metadata`, and `parse_ref`.

Solution: introduce a `ForgeBackend` class with `parse_url`,
`api_args`, and `parse_state` methods, plus a `register()` /
`backends()` registry. New forges (Gitea, Forgejo) are a single
`register()` call via the `gitea_backend()` convenience constructor.

* ci: format

spec/forge_spec.lua

@@ -186,9 +186,9 @@ describe('forge', function()
     end)
   end)
 
-  describe('_api_url', function()
-    it('builds GitHub API URL', function()
-      local url = forge._api_url({
+  describe('_api_args', function()
+    it('builds GitHub CLI args', function()
+      local args = forge._api_args({
         forge = 'github',
         owner = 'user',
         repo = 'repo',
@@ -196,11 +196,11 @@ describe('forge', function()
         number = 42,
         url = '',
       })
-      assert.equals('https://api.github.com/repos/user/repo/issues/42', url)
+      assert.same({ 'gh', 'api', '/repos/user/repo/issues/42' }, args)
     end)
 
-    it('builds GitLab API URL for issue', function()
-      local url = forge._api_url({
+    it('builds GitLab CLI args for issue', function()
+      local args = forge._api_args({
         forge = 'gitlab',
         owner = 'group',
         repo = 'project',
@@ -208,11 +208,11 @@ describe('forge', function()
         number = 15,
         url = '',
       })
-      assert.equals('https://gitlab.com/api/v4/projects/group%2Fproject/issues/15', url)
+      assert.same({ 'glab', 'api', '/projects/group%2Fproject/issues/15' }, args)
     end)
 
-    it('builds GitLab API URL for merge request', function()
-      local url = forge._api_url({
+    it('builds GitLab CLI args for merge request', function()
+      local args = forge._api_args({
         forge = 'gitlab',
         owner = 'group',
         repo = 'project',
@@ -220,11 +220,11 @@ describe('forge', function()
         number = 5,
         url = '',
       })
-      assert.equals('https://gitlab.com/api/v4/projects/group%2Fproject/merge_requests/5', url)
+      assert.same({ 'glab', 'api', '/projects/group%2Fproject/merge_requests/5' }, args)
     end)
 
-    it('builds Codeberg API URL', function()
-      local url = forge._api_url({
+    it('builds Codeberg CLI args', function()
+      local args = forge._api_args({
         forge = 'codeberg',
         owner = 'user',
         repo = 'repo',
@@ -232,7 +232,7 @@ describe('forge', function()
         number = 3,
         url = '',
       })
-      assert.equals('https://codeberg.org/api/v1/repos/user/repo/issues/3', url)
+      assert.same({ 'tea', 'api', '/repos/user/repo/issues/3' }, args)
     end)
   end)
 
@@ -316,6 +316,81 @@ describe('forge parse.body integration', function()
   end)
 end)
 
+describe('forge registry', function()
+  it('backends() returns all registered backends', function()
+    local backends = forge.backends()
+    assert.is_true(#backends >= 3)
+    local names = {}
+    for _, b in ipairs(backends) do
+      names[b.name] = true
+    end
+    assert.is_true(names['github'])
+    assert.is_true(names['gitlab'])
+    assert.is_true(names['codeberg'])
+  end)
+
+  it('register() with custom backend resolves URLs', function()
+    local custom = forge.gitea_backend({
+      name = 'mygitea',
+      shorthand = 'mg',
+      default_host = 'gitea.example.com',
+    })
+    forge.register(custom)
+
+    local ref = forge.parse_ref('https://gitea.example.com/alice/proj/issues/7')
+    assert.is_not_nil(ref)
+    assert.equals('mygitea', ref.forge)
+    assert.equals('alice', ref.owner)
+    assert.equals('proj', ref.repo)
+    assert.equals('issue', ref.type)
+    assert.equals(7, ref.number)
+  end)
+
+  it('register() with custom shorthand resolves', function()
+    local ref = forge._parse_shorthand('mg:alice/proj#7')
+    assert.is_not_nil(ref)
+    assert.equals('mygitea', ref.forge)
+    assert.equals('alice', ref.owner)
+    assert.equals('proj', ref.repo)
+    assert.equals(7, ref.number)
+  end)
+
+  it('_api_args dispatches to custom backend', function()
+    local args = forge._api_args({
+      forge = 'mygitea',
+      owner = 'alice',
+      repo = 'proj',
+      type = 'issue',
+      number = 7,
+      url = '',
+    })
+    assert.same({ 'tea', 'api', '/repos/alice/proj/issues/7' }, args)
+  end)
+
+  it('gitea_backend() creates a working backend', function()
+    local b = forge.gitea_backend({
+      name = 'forgejo',
+      shorthand = 'fj',
+      default_host = 'forgejo.example.com',
+      cli = 'forgejo-cli',
+      auth_cmd = 'forgejo-cli login',
+    })
+    assert.equals('forgejo', b.name)
+    assert.equals('fj', b.shorthand)
+    assert.equals('forgejo-cli', b.cli)
+
+    local ref = b:parse_url('https://forgejo.example.com/bob/repo/pulls/3')
+    assert.is_nil(ref)
+
+    forge.register(b)
+    ref = b:parse_url('https://forgejo.example.com/bob/repo/pulls/3')
+    assert.is_not_nil(ref)
+    assert.equals('forgejo', ref.forge)
+    assert.equals('pull_request', ref.type)
+    assert.equals(3, ref.number)
+  end)
+end)
+
 describe('forge diff integration', function()
   local store = require('pending.store')
   local diff = require('pending.diff')