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/e2e-testing/spec.md

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+## ADDED Requirements
+
+### Requirement: E2E Test Framework
+
+The system SHALL provide end-to-end tests using Playwright.
+
+#### Scenario: Test setup
+- GIVEN the e2e test directory
+- THEN `e2e/` SHALL contain Playwright configuration
+- AND tests SHALL run against the full application stack
+
+#### Scenario: Critical user journeys
+- GIVEN the e2e test suite
+- THEN it SHALL test:
+  - User login flow
+  - Project creation and listing
+  - SSH key generation
+
+#### Scenario: Test environment
+- GIVEN e2e tests are running
+- THEN they SHALL use a dedicated test database
+- AND tests SHALL clean up data after completion
+
+### Requirement: Test Commands
+
+The system SHALL provide Makefile targets for running different test categories.
+
+#### Scenario: Make targets
+- GIVEN the Makefile
+- THEN these targets SHALL exist:
+  - `make test-unit` - Run unit tests only
+  - `make test-integration` - Run integration tests only
+  - `make test-system` - Run system tests only
+  - `make test-e2e` - Run Playwright E2E tests
+  - `make test` - Run all backend tests