Issue: When `process_movie_batch` / `process_series_batch`
(apps/vod/tasks.py) creates duplicate vod_movie / vod_episode records
during a refresh, existing M3U*Relation rows get repointed to the new
records. The old UUIDs that external players (Emby / Jellyfin /
ChannelsDVR) cached in `.strm` URLs are left orphaned, and the proxy
404s on every subsequent request — even though the same request
already carries a stable `stream_id` that uniquely identifies a live
relation.
This patch makes `_get_content_and_relation` use a soft UUID lookup
and, if it misses, fall back to resolving content via
`M3UMovieRelation.stream_id` / `M3UEpisodeRelation.stream_id`. The
fallback respects the strictest match first: when
`preferred_m3u_account_id` is also present, that account is queried
first; otherwise the highest-priority active relation matching the
stream_id wins (same ordering the existing relation-selection logic
uses).
This is read-side graceful degradation, complementary to the
write-side root fix proposed in closed#973 (re-use the relation's
existing movie/series during refresh rather than rematching by TMDB
ID). The two PRs together would fully resolve#961: #973 prevents new
orphaning, this PR makes any URL that ships a stream_id survive past
orphaning. URLs without a stream_id (e.g. XC-compat
`/movie/<user>/<pass>/<id>.mkv`) are NOT covered by this patch — they
need the root fix.
Series-UUID lookups (`/proxy/vod/series/<UUID>`) are left UUID-only by
design — players cache episode and movie URLs, not series URLs. Same
pattern can be added as a follow-up if needed.
Tests: 7 new mock-based regression tests covering both branches,
verified against `:dev`. UUID-first happy path is unchanged
(M3U*Relation table never queried when the UUID resolves).
Related: #961 (open), closed#973 (root fix abandoned for inactivity).
