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-organization/spec.md

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+## ADDED Requirements
+
+### Requirement: Test Directory Structure
+
+The system SHALL organize tests into unit, integration, and system directories.
+
+#### Scenario: Directory layout
+- GIVEN the backend test suite
+- THEN `apps/api/tests/` SHALL contain:
+  - `unit/` - Pure logic tests with no external dependencies
+  - `integration/` - API endpoint tests with database
+  - `system/` - Full stack tests with external services
+
+#### Scenario: Running selective tests
+- GIVEN the test suite is organized
+- WHEN running `pytest -m unit`
+- THEN only unit tests SHALL execute
+- AND WHEN running `pytest -m integration`
+- THEN only integration tests SHALL execute
+
+### Requirement: Test Markers
+
+The system SHALL provide pytest markers for each test category.
+
+#### Scenario: Marker registration
+- GIVEN pytest configuration
+- THEN `pyproject.toml` SHALL register markers:
+  - `unit` - Fast tests with no external dependencies
+  - `integration` - Tests with database and external services
+  - `system` - End-to-end tests of the full stack
+
+#### Scenario: Marker usage
+- GIVEN a test file
+- THEN unit tests SHALL be marked with `@pytest.mark.unit`
+- AND integration tests SHALL be marked with `@pytest.mark.integration`
+- AND system tests SHALL be marked with `@pytest.mark.system`