fix: ruff UP037 — unquote the fingerprint_path return annotation

PIL's Image is imported at module scope, so the annotation never needed to
be a string.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

backend/app/utils/phash.py

@@ -112,7 +112,7 @@ def fingerprint(pil_image):
         return None
 
 
-def fingerprint_path(path) -> "Image.Image | None":
+def fingerprint_path(path) -> Image.Image | None:
     """`fingerprint` for a file on disk. None if it cannot be read — which
     the gate treats as "not a duplicate"."""
     try: