feat(docs): add offline documentation, config_help viewer, and CI pipelines

- docs/fish-config.md: curated terminal-optimized manual covering all
  public functions, keybindings, abbreviations, configuration variables,
  dependency catalog, and customization guide. Written for ov/bat/less
  readability rather than browser rendering — no callouts, no hyperlinks.
  Pandoc-compatible YAML front matter for man page compilation.

- functions/config_help.fish: viewer function with fallback chain
  ov -> bat -> man -l -> less -> cat. Accepts an optional section
  keyword to jump directly to the first matching heading.

- .gitea/workflows/man-page.yml: compiles docs/fish-config.md to
  docs/fish-config.1 via pandoc on every push to main that touches the
  source doc, then commits the result automatically.

- .gitea/workflows/docs-drift.yml: opens a reminder issue whenever
  README.md changes without a corresponding docs/fish-config.md update
  in the same push.

- README.md: documents config_help and the offline manual.
- AGENTS.md: adds Convention 10 requiring offline doc to be updated
  alongside any function, keybinding, or config change.

README.md

@@ -305,6 +305,19 @@ rm -f file.txt  # Falls through to standard rm -f
 
 `conf.d/paru-wrapper.fish` and `conf.d/yay-wrapper.fish` auto-generate thin wrapper scripts at `~/.local/bin/paru` and `~/.local/bin/yay` on first shell start (when the respective AUR helper is installed). These wrappers tee all output to timestamped log files in `SCROLLBACK_HISTORY_DIR` and prune old logs to stay under `SCROLLBACK_HISTORY_MAX_FILES`.
 
+### Offline Documentation
+
+A curated offline reference manual is available at `docs/fish-config.md`. It covers every function, keybinding, abbreviation, and configuration variable, written for terminal readability (no hyperlinks or GitHub-specific callouts).
+
+| Command | Description |
+|---|---|
+| `config_help` | Open the offline manual in the best available pager |
+| `config_help <keyword>` | Jump directly to a section matching the keyword |
+
+The viewer falls back through: **ov** (syntax highlight + section navigation) → **bat** (syntax highlight) → **man -l** (pre-compiled man page) → **less** → **cat**.
+
+Examples: `config_help keybindings` · `config_help pkg` · `config_help fish-deps` · `config_help abbreviations`
+
 ### Dependency Management
 
 `fish-deps` is a unified command for checking, installing, and updating all tools this config depends on.