fix(lint): silence ruff B007 + S110

- 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.

core/image_cache.py

@@ -198,8 +198,8 @@ class ImageCache:
             except Exception:
                 try:
                     tmp_path.unlink(missing_ok=True)
-                except Exception:
+                except Exception as cleanup_exc:
-                    pass
+                    logger.debug("image_cache tmp cleanup failed: %s", cleanup_exc)
                 raise
 
             if total <= 0:

core/torrent_clients/transmission.py

@@ -98,7 +98,7 @@ class TransmissionAdapter:
             return None
         auth = (self._username, self._password) if self._username else None
         payload = {'method': method, 'arguments': arguments}
-        for attempt in range(2):
+        for _attempt in range(2):
             try:
                 with self._session_id_lock:
                     sid = self._session_id