Deep-review round 3 of bug hunt 2026-09.
- get_or_404 / owned_or_404 answer a structured {code: "not_found", reason: <what>}
(errors.notFound.* in HU+EN, generic fallback). The structured-404 fix of round 2 had gone into the
ad-hoc `_own_playlist` (CLAUDE.md's "Not" pattern) while the shared helpers stayed string-only, so
views, tags, pins, Plex playlists, invites and users still 404'd in English. `_own_playlist` now
goes through owned_or_404; admin's hand-rolled user lookups use get_or_404.
- A move into a list that is gone names the TARGET (reason "move_target") — "this playlist doesn't
exist any more" was read as the list on screen, which still exists.
- Every refusal in the playlists router is a {code: "playlist", reason} (playlists.errors.* HU+EN)
instead of a bare English string shown verbatim in the Hungarian UI.
- `req` / `uploadReq` mark the errors they already put on screen (the error dialog, the connection
notice, the 401 sign-out), and notifyActionError skips those. The watched toggles, the saved views
and a playlist delete toasted a fault the dialog was already showing; Playlists' two hand-written
status filters now go through the same check.