fix: reorder notification DELETE routes so bulk clear matches first

FastAPI matches routes in declaration order. The DELETE /notifications
endpoint (bulk clear) was registered AFTER DELETE /notifications/{id},
so the path parameter route intercepted all requests to the bulk route,
causing a 422 UUID validation error instead of hitting clear_all.

Moved clear_all_notifications above dismiss_notification in the router.
Added regression test to verify route order.

Quality gates: pytest (22 passed)

apps/api/tests/unit/test_notifications_api_routes.py

@@ -0,0 +1,34 @@
+"""Unit tests for notification API route ordering."""
+
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+from src.api.notifications import router as notifications_router
+
+
+def test_delete_notifications_route_order() -> None:
+    """DELETE /notifications must match before DELETE /notifications/{id}.
+
+    FastAPI matches routes in declaration order. The bulk clear endpoint
+    (DELETE /notifications) must be registered before the single dismiss
+    endpoint (DELETE /notifications/{notification_id}) or the path
+    parameter route will intercept the bulk route.
+    """
+    app = FastAPI()
+    app.include_router(notifications_router)
+    client = TestClient(app)
+
+    # Verify the bulk delete route exists and returns the expected schema
+    # (it will 401 without auth, but that's fine — we just need to confirm
+    # routing doesn't hit the UUID-parameter route first)
+    response = client.delete("/notifications")
+    # Should get 401 (unauthenticated), NOT 422 (UUID parse error)
+    assert response.status_code == 401, (
+        f"Expected 401 (auth required), got {response.status_code}. "
+        f"Route order may be wrong — DELETE /notifications matched "
+        f"DELETE /notifications/{{notification_id}} instead."
+    )
+
+    # Verify the single dismiss route still works (also 401 without auth)
+    response = client.delete("/notifications/12345678-1234-1234-1234-123456789abc")
+    assert response.status_code == 401