feat: import F95 screenshot galleries with AVIF support

backend/app/gc.py

@@ -64,6 +64,8 @@ async def collect(execute=False):
             for manifest in (await db.scalars(select(VersionHistory.manifest))).all():
                 live.update(hashes(manifest))
             live.update(h for h in (await db.scalars(select(Game.cover_hash))).all() if h)
+            for gallery in (await db.scalars(select(Game.gallery_hashes))).all():
+                live.update(gallery or [])
             for key in live:
                 if not BLOB_ID_RE.fullmatch(key) or not blob_path(key).is_file():
                     raise RuntimeError(f"Missing/invalid referenced blob {key}; GC aborted")