Fix CI integration test failures

- Add proxy-body-size annotation to allow unlimited uploads via nginx
- Add requires_direct_s3 marker for tests needing direct MinIO access
- Exclude requires_direct_s3 tests from CI (can't access MinIO from outside K8s)
- Add auto-migration for tag ref_count triggers to ensure they exist

backend/tests/conftest.py

@@ -34,6 +34,10 @@ def pytest_configure(config):
         "markers",
         "slow: marks tests as slow running",
     )
+    config.addinivalue_line(
+        "markers",
+        "requires_direct_s3: marks tests that require direct S3/MinIO access (skipped in CI where S3 is not directly accessible)",
+    )
 
 
 import io