feat: implement git repository management

- Add backend API for git repository CRUD (create, list, delete)
- Support bare repository initialization and mirror cloning
- Add cascade delete for repositories when project is deleted
- Add frontend page for repository management per project
- Update project page with link to repositories
- Add repo_base_path to config
- Quality gates: ruff, mypy, typecheck, lint, build all pass

openspec/changes/archive/2025-05-18-ssh-key-management/proposal.md

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+## Why
+
+SSH keys are required for git operations with external providers. Currently the SSHKey model exists but there's no API or UI to generate, manage, or use SSH keys.
+
+## What Changes
+
+- Add backend API endpoints for SSH key CRUD operations
+- Implement Ed25519 key generation with Fernet encryption for private keys
+- Add frontend page for SSH key management
+- Display public keys with copy functionality
+
+## Capabilities
+
+### New Capabilities
+- `ssh-key-management`: Generate and manage SSH keys for git operations
+
+### Modified Capabilities
+- None
+
+## Impact
+
+- `apps/api/src/api/`: New ssh_keys.py router
+- `apps/api/src/models/ssh_key.py`: May need updates
+- `apps/web/src/`: New SSH keys page
+- `apps/api/src/main.py`: Register new router