refactor: test row factories and the fetch stub have one copy each (3109)

tests/factories.py holds image_row/make_image/make_image_async/make_tag. The
17 byte-identical _img/_tag helpers (15 modules) now import them under their
old names, so no call site changed. frontend/test/support/stubFetch.js
replaces 15 copies that differed only in formatting. Copies whose bodies
differ (other defaults, other columns, a url-only stub) are left as they
are; folding those needs a look at each caller.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

tests/test_api_gpu.py

@@ -7,20 +7,11 @@ from sqlalchemy import func, select
 from backend.app.models import GpuJob, ImageRecord
 from backend.app.services.ml.gpu_jobs import GpuJobService
 from backend.app.services.ml.regions import RegionService
+from tests.factories import make_image_async as _img
 
 pytestmark = pytest.mark.integration
 
 
-async def _img(db, sha) -> ImageRecord:
-    img = ImageRecord(
-        path=f"/images/{sha}.jpg", sha256=sha, size_bytes=1, mime="image/jpeg",
-        width=1, height=1, origin="imported_filesystem", integrity_status="unknown",
-    )
-    db.add(img)
-    await db.flush()
-    return img
-
-
 @pytest.mark.asyncio
 async def test_agent_endpoints_require_bearer(client, db):
     resp = await client.post("/api/gpu/jobs/lease", json={"agent_id": "a1"})