feat: add pytest testing dashboard with run history and statistics

Add a new Testing Dashboard page that replaces the old Testing Hub with
pytest integration:

- Database models for test runs, results, and collections (TestRun,
  TestResult, TestCollection)
- Test runner service that executes pytest with JSON reporting and
  stores results in the database
- REST API endpoints for running tests, viewing history, and statistics
- Dashboard UI showing pass rates, trends, tests by category, and top
  failing tests
- Alembic migration for the new test_* tables

The dashboard allows admins to:
- Run pytest directly from the UI
- View test run history with pass/fail statistics
- See trend data across recent runs
- Identify frequently failing tests
- Collect test information without running

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/admin/__init__.py

@@ -37,6 +37,7 @@ from . import (
     notifications,
     products,
     settings,
+    tests,
     users,
     vendor_domains,
     vendor_products,
@@ -142,5 +143,10 @@ router.include_router(
     code_quality.router, prefix="/code-quality", tags=["admin-code-quality"]
 )
 
+# Include test runner endpoints
+router.include_router(
+    tests.router, prefix="/tests", tags=["admin-tests"]
+)
+
 # Export the router
 __all__ = ["router"]