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-test-infrastructure-improvements/specs/test-isolation/spec.md

@@ -0,0 +1,38 @@
+## ADDED Requirements
+
+### Requirement: Shared Test Fixtures
+
+The system SHALL provide shared fixtures in `conftest.py` for common test needs.
+
+#### Scenario: Database session fixture
+- GIVEN an integration test
+- WHEN using the `db_session` fixture
+- THEN it SHALL provide an async SQLAlchemy session
+- AND the session SHALL use transaction rollback for isolation
+
+#### Scenario: Test client fixture
+- GIVEN an API integration test
+- WHEN using the `client` fixture
+- THEN it SHALL provide an authenticated TestClient instance
+- AND the client SHALL have valid access and refresh tokens
+
+#### Scenario: SQLite unit test database
+- GIVEN a unit test
+- WHEN the test uses the `db_engine` fixture
+- THEN it SHALL provide an in-memory SQLite engine
+- AND no PostgreSQL connection SHALL be required
+
+### Requirement: Transaction Isolation
+
+The system SHALL ensure integration tests don't pollute the database.
+
+#### Scenario: Rollback after test
+- GIVEN an integration test creates data
+- WHEN the test completes
+- THEN all database changes SHALL be rolled back
+- AND subsequent tests SHALL see a clean database state
+
+#### Scenario: Parallel test safety
+- GIVEN multiple integration tests run concurrently
+- WHEN each test uses transaction isolation
+- THEN tests SHALL not interfere with each other