test(phase-03): remove stale xfail markers from quota tests

test_quota_increment_atomic and test_quota_exceeded_response were marked
xfail for PostgreSQL but pass on SQLite — markers removed, tests now PASSED.
Concurrent race and delete decrement keep xfail; they require real PG locking.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/test_quota.py

@@ -9,11 +9,12 @@ Requirements covered:
 
 Note on SQLite compatibility:
   The atomic quota SQL uses PostgreSQL-specific features (GREATEST, RETURNING).
-  SQLite also stores UUIDs without dashes (CHAR(32)) while the SQL text uses str(uuid)
-  (dashed format). These tests are marked xfail(strict=False) so they xpass on
-  PostgreSQL (INTEGRATION=1) and are tolerated as xfail on SQLite unit test runs.
-  The endpoint implementation is correct for PostgreSQL — the xfail is a test-env
-  limitation, not a code defect.
+  test_quota_increment_atomic and test_quota_exceeded_response pass on SQLite because
+  their code paths use parameterized ORM queries that work in both DBs.
+  test_concurrent_quota_race and test_delete_decrements_quota remain xfail(strict=False):
+  the concurrent race requires PostgreSQL row-level locking semantics, and the delete
+  decrement hits a SQLite UUID format mismatch in the GREATEST() WHERE clause.
+  These are test-env limitations, not code defects.
 """
 from __future__ import annotations
 
@@ -36,7 +37,6 @@ async def _set_doc_user_id(db_session, doc_id_str: str, user_id) -> None:
     await db_session.commit()
 
 
-@pytest.mark.xfail(strict=False, reason="requires PostgreSQL for atomic UUID-typed quota SQL")
 async def test_quota_increment_atomic(
     async_client, db_session, auth_user, mock_minio_presigned, mock_minio_stat, monkeypatch
 ):
@@ -136,7 +136,6 @@ async def test_concurrent_quota_race(
     assert success_count == 1, f"Both succeeded — quota double-spend! statuses: {statuses}"
 
 
-@pytest.mark.xfail(strict=False, reason="requires PostgreSQL for atomic UUID-typed quota SQL")
 async def test_quota_exceeded_response(
     async_client, db_session, auth_user, mock_minio_presigned, mock_minio_stat, monkeypatch
 ):