docs: restructure vimdoc with integrations parent section

Problem: integration docs (fugitive, neogit, gitsigns) were scattered
as top-level sections with no grouping, making it hard to find all
supported plugin integrations in one place.

Solution: add `|diffs-integrations|` parent section that groups all
integration subsections under a single TOC entry.

doc/diffs.nvim.txt

@@ -6,22 +6,27 @@ License: MIT
 ==============================================================================
 INTRODUCTION                                                       *diffs.nvim*
 
-diffs.nvim adds syntax highlighting to diff views. It overlays language-aware
+diffs.nvim adds language-aware syntax highlighting to unified diff content
-highlights on top of default diff highlighting in vim-fugitive, Neogit, and
+in Neovim buffers. It replaces flat `diffAdded`/`diffRemoved` coloring with
-Neovim's built-in diff mode.
+treesitter syntax, blended line backgrounds, and character-level intra-line
+diffs.
+
+With no configuration, diffs.nvim provides:
+- `gitcommit` diff highlighting (e.g., `git commit --verbose`)
+- Inline merge conflict detection, highlighting, and resolution
+- Background-only diff colors for `&diff` buffers (vimdiff, diffthis)
+
+All other integrations are opt-in. See |diffs-integrations|.
 
 Features: ~
-- Syntax highlighting in |:Git| summary diffs and commit detail views
+- Treesitter syntax highlighting in diff hunks
-- Diff header highlighting (`diff --git`, `index`, `---`, `+++`)
+- Character-level intra-line diff highlighting
-- Syntax highlighting in |:Gdiffsplit| / |:Gvdiffsplit| side-by-side diffs
-- |:Gdiff| command for unified diff against any git revision
-- gitsigns.nvim blame popup highlighting (see |diffs-gitsigns|)
-- Background-only diff colors for any `&diff` buffer (vimdiff, diffthis, etc.)
 - Vim syntax fallback for languages without a treesitter parser
 - Blended diff background colors that preserve syntax visibility
 - Optional diff prefix (`+`/`-`/` `) concealment
 - Gutter (line number) highlighting
-- Inline merge conflict marker detection, highlighting, and resolution
+- |:Gdiff| unified diff against any revision
+- Email quoting/patch syntax support (`> diff ...`)
 
 ==============================================================================
 CONTENTS                                                      *diffs-contents*
@@ -32,43 +37,40 @@ CONTENTS                                                      *diffs-contents*
   4. Configuration ............................................ |diffs-config|
   5. Commands ............................................... |diffs-commands|
   6. Mappings ............................................... |diffs-mappings|
-  7. Fugitive Status Keymaps ................................ |diffs-fugitive|
+  7. Integrations ..................................... |diffs-integrations|
+       Fugitive .......................................... |diffs-fugitive|
+       Neogit .............................................. |diffs-neogit|
+       Gitsigns .......................................... |diffs-gitsigns|
   8. Conflict Resolution .................................... |diffs-conflict|
   9. Merge Diff Resolution ..................................... |diffs-merge|
- 10. Neogit ................................................... |diffs-neogit|
+ 10. API ......................................................... |diffs-api|
- 11. Gitsigns ................................................ |diffs-gitsigns|
+ 11. Implementation ................................... |diffs-implementation|
- 12. API ......................................................... |diffs-api|
+ 12. Known Limitations ................................... |diffs-limitations|
- 13. Implementation ................................... |diffs-implementation|
+ 13. Highlight Groups ..................................... |diffs-highlights|
- 14. Known Limitations ................................... |diffs-limitations|
+ 14. Health Check ............................................. |diffs-health|
- 15. Highlight Groups ..................................... |diffs-highlights|
+ 15. Acknowledgements ............................... |diffs-acknowledgements|
- 16. Health Check ............................................. |diffs-health|
- 17. Acknowledgements ............................... |diffs-acknowledgements|
 
 ==============================================================================
 REQUIREMENTS                                              *diffs-requirements*
 
 - Neovim 0.9.0+
-- vim-fugitive (https://github.com/tpope/vim-fugitive) (optional, for unified
-  diff syntax highlighting in |:Git| and commit views)
 - Treesitter parsers for languages you want highlighted
 
-Note: The diff mode feature (background-only colors for |:diffthis|, vimdiff,
-etc.) works without vim-fugitive.
-
 ==============================================================================
 SETUP                                                            *diffs-setup*
 
 Install with lazy.nvim: >lua
-    {
+    { 'barrettruth/diffs.nvim' }
-      'barrettruth/diffs.nvim',
-      dependencies = { 'tpope/vim-fugitive' },
-    }
 <
-The plugin works automatically with no configuration required. For
-customization, see |diffs-config|.
 
-NOTE: Load your colorscheme before `diffs.nvim`. For example, with lazy.nvim,
+Do not lazy load with `event`, `lazy`, `ft`, `config`, or `keys` —
-set `priority = 1000` and `lazy = false` on your colorscheme plugin.
+diffs.nvim lazy-loads itself.
+
+NOTE: Load your colorscheme before diffs.nvim. With lazy.nvim, set
+`priority = 1000` and `lazy = false` on your colorscheme plugin.
+
+See |diffs-config| for customization, |diffs-integrations| for plugin
+support.
 
 ==============================================================================
 CONFIGURATION                                                   *diffs-config*
@@ -81,6 +83,7 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
       fugitive = false,
       neogit = false,
       gitsigns = false,
+      committia = false,
       extra_filetypes = {},
       highlights = {
         background = true,
@@ -174,6 +177,16 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                                  vim.g.diffs = { gitsigns = true }
 <
 
+        {committia}          (boolean|table, default: false)
+                             Enable committia.vim integration. Pass `true`
+                             or `{}` to enable, `false` to disable. When
+                             active, committia's diff pane (`ft=git`,
+                             buffer name `__committia_diff__`) receives
+                             treesitter syntax, line backgrounds, and
+                             intra-line diffs. >lua
+                                 vim.g.diffs = { committia = true }
+<
+
         {extra_filetypes}    (table, default: {})
                              Additional filetypes to attach to, beyond the
                              built-in `git`, `gitcommit`, and any enabled
@@ -184,6 +197,12 @@ Configuration is done via `vim.g.diffs`. Set this before the plugin loads:
                                    extra_filetypes = { 'diff' },
                                  }
 <
+                             Adding `'diff'` also enables highlighting in
+                             picker preview buffers that set `filetype=diff`:
+                             telescope.nvim (git_commits, git_bcommits,
+                             git_status), snacks.nvim (syntax style only),
+                             and fzf-lua (builtin previewer only). Terminal-
+                             based previewers are not supported.
 
         {highlights}         (table, default: see below)
                              Controls which highlight features are enabled.
@@ -447,10 +466,44 @@ Diff buffer mappings: ~
                     or the fugitive status keymaps.
 
 ==============================================================================
-FUGITIVE STATUS KEYMAPS                                   *diffs-fugitive*
+INTEGRATIONS                                           *diffs-integrations*
 
-When inside a vim-fugitive |:Git| status buffer, diffs.nvim provides keymaps
+diffs.nvim integrates with several plugins. There are two attachment
-to open unified diffs for files or entire sections.
+patterns:
+
+Automatic: ~
+Enable via config toggles. The plugin registers `FileType` autocmds for
+each integration's filetypes and attaches automatically.
+>lua
+    vim.g.diffs = {
+      fugitive = true,
+      neogit = true,
+      gitsigns = true,
+    }
+<
+
+Opt-in: ~
+For filetypes not covered by a built-in integration, use `extra_filetypes`
+to attach to any buffer whose content looks like a diff.
+>lua
+    vim.g.diffs = { extra_filetypes = { 'diff' } }
+<
+
+------------------------------------------------------------------------------
+FUGITIVE                                                      *diffs-fugitive*
+
+Enable vim-fugitive (https://github.com/tpope/vim-fugitive) support: >lua
+    vim.g.diffs = { fugitive = true }
+<
+
+|:Git| status and commit views receive treesitter syntax, line backgrounds,
+and intra-line diffs. |:Gdiff| opens a unified diff against any revision
+(see |diffs-commands|).
+
+Fugitive status keymaps: ~
+
+When inside a |:Git| status buffer, diffs.nvim provides keymaps to open
+unified diffs for files or entire sections.
 
 Keymaps: ~
                                                           *diffs-du* *diffs-dU*
@@ -499,6 +552,31 @@ Configuration: ~
                              Keymap for unified diff in vertical split.
                              Set to `false` to disable.
 
+------------------------------------------------------------------------------
+NEOGIT                                                          *diffs-neogit*
+
+Enable Neogit (https://github.com/NeogitOrg/neogit) support: >lua
+    vim.g.diffs = { neogit = true }
+<
+
+Expanding a diff in a Neogit buffer (e.g., TAB on a file in the status
+view) applies treesitter syntax highlighting and intra-line diffs to the
+hunk lines.
+
+------------------------------------------------------------------------------
+GITSIGNS                                                      *diffs-gitsigns*
+
+Enable gitsigns.nvim (https://github.com/lewis6991/gitsigns.nvim) blame
+popup highlighting: >lua
+    vim.g.diffs = { gitsigns = true }
+<
+
+`:Gitsigns blame_line full=true` popups receive treesitter syntax, line
+backgrounds, and intra-line diffs.
+
+Highlights are applied in a separate `diffs-gitsigns` namespace and do not
+interfere with the main decoration provider used for diff buffers.
+
 ==============================================================================
 CONFLICT RESOLUTION                                          *diffs-conflict*
 
@@ -642,52 +720,6 @@ The working file buffer is modified in place; save it when ready.
 Phase 1 inline conflict highlights (see |diffs-conflict|) are refreshed
 automatically after each resolution.
 
-==============================================================================
-NEOGIT                                                          *diffs-neogit*
-
-diffs.nvim works with Neogit (https://github.com/NeogitOrg/neogit) out of
-the box. Enable Neogit support in your config: >lua
-    vim.g.diffs = { neogit = true }
-<
-
-When a diff is expanded in a Neogit buffer (e.g., via TAB on a file in the
-status view), diffs.nvim applies treesitter syntax highlighting and
-intra-line diffs to the hunk lines, just as it does for fugitive.
-
-Neogit highlight overrides: ~
-On first attach to a Neogit buffer, diffs.nvim overrides Neogit's diff
-highlight groups (`NeogitDiffAdd*`, `NeogitDiffDelete*`,
-`NeogitDiffContext*`, `NeogitHunkHeader*`, `NeogitDiffHeader*`, etc.) by
-setting them to empty (`{}`). This gives diffs.nvim sole control of diff
-line visuals. The overrides are reapplied on `ColorScheme` since Neogit
-re-defines its groups then. When `neogit = false`, no highlight overrides
-are applied.
-
-==============================================================================
-GITSIGNS                                                      *diffs-gitsigns*
-
-diffs.nvim can enhance gitsigns.nvim blame popups with syntax highlighting.
-Enable gitsigns support in your config: >lua
-    vim.g.diffs = { gitsigns = true }
-<
-
-When `:Gitsigns blame_line full=true` opens a popup, diffs.nvim intercepts
-the popup and replaces gitsigns' flat `GitSignsAddPreview`/
-`GitSignsDeletePreview` highlights with:
-
-- Treesitter syntax highlighting on the code content
-- `DiffsAdd`/`DiffsDelete` line backgrounds
-- Character-level intra-line diffs (`DiffsAddText`/`DiffsDeleteText`)
-- `@diff.plus`/`@diff.minus` coloring on `+`/`-` prefix characters
-
-The integration patches `gitsigns.popup.create` and `gitsigns.popup.update`
-so highlights persist across gitsigns' two-phase render (initial popup, then
-update with GitHub/PR data). If gitsigns loads after diffs.nvim, a
-`User GitAttach` autocmd retries the setup automatically.
-
-Highlights are applied in a separate `diffs-gitsigns` namespace and do not
-interfere with the main decoration provider used for diff buffers.
-
 ==============================================================================
 API                                                                *diffs-api*