docs: Add CLI documentation and version flag support (#46)

## Summary

Adds CLI documentation infrastructure and improves CLI usability:

- **CLI**: `g --version` / `g -V` now shows g's version (previously passed to VCS)
- **Documentation**: New [CLI documentation page](https://g.git-pull.com/cli/) with complete command reference
- **Documentation**: Linkable argument anchors (headerlinks) for easy sharing
- **Documentation**: Semantic CLI markup roles and syntax highlighting

## User-facing changes

### CLI
- `g --version` and `g -V` display g's version instead of being passed to the underlying VCS
- Documentation now accurately describes this behavior

### Documentation
- New CLI page at `/cli/` with argparse-generated command reference
- CLI arguments have linkable anchors (¶ headerlinks)
- Improved CSS for light/dark mode compatibility

## Technical changes

- Added `docs/_ext/sphinx_argparse_neo/` - argparse documentation with headerlinks
- Added `docs/_ext/argparse_lexer.py` - syntax highlighting for CLI output
- Added `docs/_ext/argparse_roles.py` - semantic markup roles (`:cli-opt:`, `:cli-cmd:`, etc.)
- Added `docs/_ext/argparse_exemplar.py` - epilog examples transformation
- Added `docs/_static/css/argparse-highlight.css` - CLI styling
- Added comprehensive test suite in `tests/docs/_ext/`
- Updated `docs/conf.py` with extension configuration
- Updated `pyproject.toml` with mypy overrides

Author: tony

AGENTS.md

@@ -17,7 +17,7 @@ g is a lightweight CLI wrapper that proxies to the current directory's VCS comma
 
 Key features:
 - Detects VCS by walking parent directories and mapping `.git`, `.svn`, or `.hg`
-- Proxies CLI arguments directly to the detected VCS binary
+- Proxies CLI arguments to the detected VCS binary (--version/-V is handled by g)
 - Minimal surface area: primary logic lives in `src/g/__init__.py`
 - Test fixtures cover CLI behavior for both repo and non-repo directories
 

CHANGES

@@ -33,7 +33,25 @@ $ uvx --from 'g' --prerelease allow g
 _Notes on upcoming releases will be added here_
 <!-- END PLACEHOLDER - ADD NEW CHANGELOG ENTRIES BELOW THIS LINE -->
 
-<!-- Maintainers, insert changes / features for the next release here -->
+### CLI
+
+- `g --version` and `g -V` now display g's version instead of being passed to
+  the underlying VCS (#46)
+
+  This makes it easier to check which version of g you have installed:
+
+  ```console
+  $ g --version
+  g 0.0.10
+  ```
+
+### Documentation
+
+- Add [CLI documentation page](https://g.git-pull.com/cli/) with complete
+  command reference (#46)
+
+- CLI argument documentation now has linkable anchors (headerlinks) for easy
+  sharing and reference (#46)
 
 ## g 0.0.9 (2026-01-24)
 

docs/_ext/__init__.py

@@ -0,0 +1,3 @@
+"""Sphinx extensions for g documentation."""
+
+from __future__ import annotations