## Why

Projects exist but users cannot create or manage git repositories. The platform needs to allow users to create bare repositories, clone external ones, and manage them within projects.

## What Changes

- Add backend API for git repository CRUD operations
- Implement bare repository initialization on disk
- Support cloning external repositories as mirrors
- Add frontend page for repository management
- Integrate with existing project structure

## Capabilities

### New Capabilities
- `git-repo-management`: Full git repository lifecycle within projects

### Modified Capabilities
- `project-management`: Include repositories in project responses

## Impact

- New API endpoints under `/projects/{id}/repositories`
- Disk storage at `/data/repos/{user_id}/{project_id}/{repo_name}.git`
- Frontend repository list and creation UI
