test(allowlist): unique image paths in coverage tests (CI fix)

The new coverage tests' sequential shas (c{i:063d}) share their first 8 chars,
so deriving the image path from sha[:8] collided on uq_image_record_path. Use
the full sha in the path. Same hardening for test_api_suggestions._img.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XCUHUGQLrBrkgyk1t49kpX

tests/test_api_suggestions.py

@@ -18,7 +18,7 @@ async def _img(db, preds, sha="s" * 64):
     from tests._prediction_helpers import seed_predictions
 
     img = ImageRecord(
-        path=f"/images/{sha[:8]}.jpg", sha256=sha, size_bytes=1,
+        path=f"/images/{sha}.jpg", sha256=sha, size_bytes=1,
         mime="image/jpeg", width=1, height=1,
         origin="imported_filesystem", integrity_status="unknown",
     )