Fix review findings and remove Uncategorized from sidebar

Backend: cache Google access tokens (drop dead access_token_expires_at,
migration 0007), handle MeTube cleared/canceled events by URL, return
email from /auth/status only when authenticated, move Google base URLs
into settings, run container as non-root.

Frontend: include local feed filters in the query key, remove dead
Saved page and unused assets, drop stale CategoryNav props and classes,
send Content-Type only with a body, remove Uncategorized from sidebar.

backend/app/services/metube_client.py

@@ -10,7 +10,10 @@ Verified against the real MeTube source (alexta69/metube, app/main.py + app/ytdl
   JSON-*string*-encoded (json.JSONEncoder().encode(...)), not a raw object — must
   json.loads() the payload. Relevant keys: id, title, url, status, msg, percent
   (float 0-100 or None), filename (already relative to DOWNLOAD_DIR), error.
-  'canceled'/'cleared' carry just an id (also JSON-string-encoded).
+  'canceled'/'cleared' carry the download's URL key (JSON-string-encoded),
+  one event per item; 'cleared' fires only when a done entry is deleted
+  (trash via /delete?where=done or CLEAR_COMPLETED_AFTER) — clearing the
+  queue emits 'canceled'.
 - MeTube status vocabulary: pending/preparing/scheduled/downloading/postprocessing/
   finished/error — mapped to our own vocabulary in sync with download_jobs.
 - GET /history returns {"queue": [...], "pending": [...], "done": [...]} of the