Items can exist in the media server but be absent from Sonarr (deleted,
never added, or movies mis-classified as shows by Jellyfin/Emby). For
show-level properties whose semantics are intrinsic to the show rather
than to Sonarr's local state, the Sonarr getter now falls back to the
configured metadata provider after a confirmed Sonarr miss.

- Fallback set: `ended`, `firstAirDate` (show-level), `seasons`
  (show-level, specials-filtered to match Sonarr's `statistics.seasonCount`).
- Excluded by design: `status`, `originalLanguage`, `rating` —
  provider vocabularies / scales don't compare to Sonarr's. Sonarr-only
  state (`monitored`, `tags`, `filePath`, `diskSize*`, …) also stays null.
- TVDB extended series interface gains `seasons[]` typing so the count
  can be filtered to the default ordering before excluding Season 0.
- "Not in Sonarr/Radarr" warns now end with "Is the series/movie tracked
  in Sonarr/Radarr?" to prompt the user.

Sonarr is always primary; fallback only fires on the empty `getSeriesByTvdbId`
return, and the existing ArrLookupCache still dedupes the miss per run.