- core/torrent_clients/transmission.py: rename unused loop var
`attempt` to `_attempt` in the session-id renegotiation loop
(B007 — loop var not used in body).
- core/image_cache.py: log the cleanup exception instead of
swallowing it silently (S110 — bare try/except/pass). debug
level since a failed tmp unlink is non-fatal; the outer
``raise`` still propagates the original error.
Full ruff sweep clean.
Add a disk-backed image cache with hashed browser URLs, SQLite metadata, size/type validation, stale fallback, and per-image fetch locking. Route normalized artwork through /api/image-cache while keeping /api/image-proxy as a compatibility shim, and align browser max-age with the image cache TTL. Add focused tests for cache behavior and image URL normalization.