feat(docs): add auto-generated Markdown wiki

Adds docs/split-wiki.py, a Python script that splits fish-config.md
into a multi-page Markdown wiki under docs/wiki/:

- index.md: DESCRIPTION intro + full section ToC
- one file per numbered section (1-configuration-variables.md … 9-viewing-this-manual.md)
- each section page has a nav bar at the top linking to every other section

The build-docs.yml workflow now runs the script alongside pandoc so all
three formats (man page, HTML, wiki) are regenerated together from a
single source in one CI run.

README slimmed down to a pointer to the wiki; docs/fish-config.md §9
gains an "As a wiki" subsection.

docs/wiki/index.md

@@ -0,0 +1,38 @@
+# Fish Shell Configuration
+
+A production-grade Fish shell configuration targeting Fish 4.x. It provides:
+
+- Drop-in replacements for common Unix tools (ls, cat, rm, du, ping, less)
+- Deep Kitty and WezTerm terminal integration: tab/window/pane management from
+  the command line
+- Scrollback history snapshots saved to ~/.terminal_history on session exit
+- Automatic Python virtualenv activation on directory change
+- Cross-platform package management via pkg and fish-deps
+- AI session helpers for Claude Code and Antigravity
+- Catppuccin Mocha color theme throughout
+
+The configuration is split across:
+
+    config.fish          Main entry point; sets env vars and PATH
+    conf.d/              Auto-sourced fragments: keybindings, abbreviations,
+                         theme, starship, zoxide, wakatime
+    functions/           One function per file, autoloaded by Fish
+    completions/         Tab completion scripts
+    integrations/        FZF Catppuccin theme and bindings
+    docs/                This offline documentation and compiled man page
+
+---
+
+---
+
+## Table of Contents
+
+- [1. Configuration Variables](1-configuration-variables.md)
+- [2. Path Setup](2-path-setup.md)
+- [3. Key Bindings](3-key-bindings.md)
+- [4. Abbreviations](4-abbreviations.md)
+- [5. Functions Reference](5-functions-reference.md)
+- [6. Dependency Catalog](6-dependency-catalog.md)
+- [7. Customization](7-customization.md)
+- [8. Fisher Plugins](8-fisher-plugins.md)
+- [9. Viewing This Manual](9-viewing-this-manual.md)