Add configurable commit message styles

[camUrban]

Summary

• Add a style system that lets users configure commit message formats (e.g., conventional commits, simple) instead of relying solely on git history auto-detection
• Ship two built-in styles (conventional and simple) and support user-created custom styles stored in ~/.claude-commit/styles/
• Add claude-commit style sub-command for managing styles (list, show, set, clear, create, delete) and a --style CLI flag for per-run overrides

Changes

• config.py: Add style management methods: get/set/clear default style, list available styles (bundled+user), read style content, and create/delete custom styles
• main.py: Wire style system into commit generation: resolve style from CLI flag or config, inject style instructions into the system prompt, and skip git history detection when a style is active. Add style sub-command handler and
  --style/-s argument
• styles/conventional.txt: Built-in conventional commits style definition
• styles/simple.txt: Built-in simple/plain style definition
• pyproject.toml: Include styles/*.txt as package data

[JohannLai]

Thanks for the PR! The style system is a nice feature — clean API design with good layering (CLI flag > config default > auto-detect). A few things to address before merging:

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Bug: console.print() with file=sys.stderr

In main(), the style-not-found error block uses:

console.print(f"[red]❌ Style '{style_name}' not found.[/red]", file=sys.stderr)
console.print("[yellow]   Run ...[/yellow]", file=sys.stderr)

Rich's Console.print() does not accept a file keyword — this will raise a TypeError at runtime. Should use error_console.print() instead (which is already configured with stderr=True).

Inconsistency: get_user_styles_dir() ignores custom config_path

Config.__init__ accepts a config_path parameter (used heavily in tests), but get_user_styles_dir() hardcodes Path.home() / ".claude-commit" / "styles". This means tests that use tmp_path for config will still read/write styles from the real home directory.

Suggest deriving from self.config_path.parent:

def get_user_styles_dir(self) -> Path:
    return self.config_path.parent / "styles"

Missing tests

The project now has a test suite (tests/). This PR should include tests for the new config methods (get_style, set_style, clear_style, list_styles, create_custom_style, delete_custom_style) and the handle_style_command function. Most of these are pure logic and straightforward to test.

Minor: handle_style_command doesn't use error_console

handle_alias_command uses print(..., file=sys.stderr) for errors (which works), but for consistency with the rest of the codebase you might want to keep the same pattern. Not a blocker.

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Overall the design is solid — the style override injection into the system prompt and the conditional step1 logic both make sense. Just the file=sys.stderr bug needs fixing before merge.

[JohannLai]

Also, sorry about the conflicts — I recently added a test suite and refactored some helpers in main.py, which will likely require rebasing your branch. Apologies for the extra work! 🙏