MAESTRO: fix async tests router validation

Auto Run Docs/SpecKit-web-header-analyzer-Phase-04-Test-Selection.md

@@ -28,7 +28,7 @@ This phase implements the test selection panel and analysis configuration contro
 
 ## Completion
 
-- [ ] `pytest backend/tests/api/test_tests_router.py` passes
+- [x] `pytest backend/tests/api/test_tests_router.py` passes
 - [ ] `GET /api/tests` returns all 106+ tests with id, name, and category
 - [x] All vitest tests pass: `npx vitest run src/__tests__/TestSelector.test.tsx src/__tests__/AnalysisControls.test.tsx`
 - [ ] Test selector renders all 106+ tests with checkboxes

backend/app/routers/tests.py

@@ -12,4 +12,4 @@ router = APIRouter(prefix="/api", tags=["tests"])
 def list_tests() -> list[TestResponse]:
     registry = ScannerRegistry()
     tests = registry.list_tests()
-    return [TestResponse.model_validate(test) for test in tests]
+    return [TestResponse.model_validate(test.model_dump()) for test in tests]

backend/tests/api/test_tests_router.py

@@ -7,7 +7,7 @@ from app.engine.scanner_registry import ScannerRegistry
 from app.main import app
 
 
-@pytest.mark.asyncio
+@pytest.mark.anyio
 async def test_get_tests_returns_all_registered_tests() -> None:
     registry = ScannerRegistry()
     expected = registry.list_tests()