feat(commands): add AI git commit message generator

Add comprehensive slash command for generating conventional commit
messages using AI. The command analyzes staged git changes and creates
well-structured commit messages following best practices.

Features:
- Conventional commit format (type, scope, description)
- Interactive message editing and regeneration
- Context-aware analysis of git diffs
- Learning from existing commit history style
- Support for custom type and scope hints
- Multi-step workflow with user confirmation

Command supports multiple usage patterns:
- Basic: /git-commit-msg
- With hints: /git-commit-msg fix
- With context: /git-commit-msg "feat(api)"

Also updates command README with documentation for the new command.

🤖 Generated with Claude Code

.claude/commands/README.md

@@ -54,6 +54,16 @@ Create a comprehensive synthesis of the week's work.
 
 Best for: Weekly reviews, pattern recognition
 
+### 💬 git-commit-msg
+
+AI-generated conventional commit messages from staged changes.
+
+```
+/git-commit-msg
+```
+
+Best for: Creating meaningful commit messages, maintaining clean git history
+
 ## Creating Custom Commands
 
 1. Create a new `.md` file in this directory