feat(archive): duration syntax and confirmation prompt (#113)

* feat(s3): create bucket interactively during auth when unconfigured

Problem: when a user runs `:Pending s3 auth` with no bucket configured,
auth succeeds but offers no way to create the bucket. The user must
manually run `aws s3api create-bucket` and update their config.

Solution: add `util.input()` coroutine-aware prompt wrapper and a
`create_bucket()` flow in `s3.lua` that prompts for bucket name and
region, handles the `us-east-1` LocationConstraint quirk, and logs a
config snippet on success. Called automatically from `auth()` when
`sync.s3.bucket` is absent.

* ci: typing

* feat(parse): add `parse_duration_to_days` for duration string conversion

Problem: The archive command accepted only a bare integer for days,
inconsistent with the `+Nd`/`+Nw`/`+Nm` duration syntax used elsewhere.

Solution: Add `parse_duration_to_days()` supporting `Nd`, `Nw`, `Nm`,
and bare integers. Returns nil on invalid input for caller error handling.

* feat(archive): duration syntax and confirmation prompt

Problem: `:Pending archive` accepted only a bare integer for days and
silently deleted tasks with no confirmation, risking accidental data loss.

Solution: Accept duration strings (`7d`, `3w`, `2m`) via
`parse.parse_duration_to_days()`, show a `vim.ui.input` confirmation
prompt before removing tasks, and skip the prompt when zero tasks match.

plugin/pending.lua

@@ -203,6 +203,9 @@ end, {
       end
       return filtered
     end
+    if cmd_line:match('^Pending%s+archive%s') then
+      return filter_candidates(arg_lead, { '7d', '2w', '30d', '3m', '6m', '1y' })
+    end
     if cmd_line:match('^Pending%s+done%s') then
       local store = require('pending.store')
       local s = store.new(store.resolve_path())