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.

functions/config_help.fish

@@ -0,0 +1,75 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# SYNOPSIS
+#   config_help [section]
+#
+# DESCRIPTION
+#   Opens the offline fish shell configuration manual in the best available
+#   pager. Falls back through ov -> bat -> man -> less -> cat.
+#   If a section keyword is provided, the pager opens at the first heading
+#   that matches the keyword (case-insensitive).
+#
+# ARGUMENTS
+#   section  Optional keyword to jump to a matching section heading
+#
+# RETURNS
+#   0  Manual displayed
+#   1  Documentation file not found
+#
+# EXAMPLE
+#   config_help
+#   config_help keybindings
+#   config_help pkg
+#   config_help fish-deps
+function config_help --description 'Open the offline fish shell configuration manual'
+    set -l doc_file "$__fish_config_dir/docs/fish-config.md"
+    set -l man_file "$__fish_config_dir/docs/fish-config.1"
+
+    if not test -f "$doc_file"
+        set_color red
+        echo "error: documentation not found at $doc_file" >&2
+        set_color normal
+        return 1
+    end
+
+    # ── Resolve section start line ───────────────────────────────
+    set -l start_line 1
+    if test -n "$argv[1]"
+        set -l found (grep -n -im 1 "^#\+.*$argv[1]" "$doc_file" | cut -d: -f1)
+        if test -n "$found"
+            set start_line $found
+        else
+            set_color yellow
+            echo "note: no section matching '$argv[1]' — opening at top" >&2
+            set_color normal
+        end
+    end
+
+    # ── Viewer fallback chain ────────────────────────────────────
+    if type -q ov
+        ov --syntax --syntax-name markdown \
+           --section-delimiter "^#" \
+           --section-header \
+           +"$start_line" "$doc_file"
+
+    else if type -q bat
+        if test $start_line -gt 1
+            # bat can't jump to a line in paging mode; show a hint instead
+            set_color brblack
+            echo "note: bat pager active — use / to search for your section" >&2
+            set_color normal
+        end
+        bat --language=markdown --paging=always "$doc_file"
+
+    else if test -f "$man_file"
+        # Pre-compiled man page as a pager-independent fallback
+        man -l "$man_file"
+
+    else if type -q less
+        less +"$start_line" "$doc_file"
+
+    else
+        cat "$doc_file"
+    end
+end