fix(fc5): ruff (E712, ASYNC230/240, I001) + Credential.credential_type + FileStorage in api_migrate test

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/services/migrators/verify.py

@@ -18,7 +18,7 @@ async def verify_async(db: AsyncSession, *, expected: dict | None = None) -> dic
 
     checks = {
         "artist_subscriptions": (
-            select(func.count(Artist.id)).where(Artist.is_subscription == True)
+            select(func.count(Artist.id)).where(Artist.is_subscription.is_(True))
         ),
         "source_count": select(func.count(Source.id)),
         "credential_count": select(func.count(Credential.id)),
@@ -51,12 +51,15 @@ async def verify_sha256_sample(
     samples: list[dict] = []
     for img_id, path, expected_sha in rows:
         p = Path(path)
-        if not p.exists():
+        # Sync stdlib filesystem ops are intentional: this verify pass runs
+        # inside a Celery task under asyncio.run; no other awaitables compete
+        # for the loop. Same pattern as download_service.py.
+        if not p.exists():  # noqa: ASYNC240
             missing += 1
             samples.append({"id": img_id, "path": path, "result": "missing"})
             continue
         h = hashlib.sha256()
-        with p.open("rb") as f:
+        with p.open("rb") as f:  # noqa: ASYNC230
             for chunk in iter(lambda: f.read(65536), b""):
                 h.update(chunk)
         if h.hexdigest() == expected_sha: