Removes the last YouTube-specific routes (/youtube/*) and merges them
into the general track/album/playlist endpoints, keyed by a `source`
string validated against TrackSource. This mirrors the earlier track
search merge for albums and playlist-track additions:
- GetAlbums now merges local albums with live YouTube Music search
results, paginated via a youtubeContinuationToken, deduped against
already-materialized ExternalAlbum rows.
- New GET /albums/external/{source}/{externalId} and
GET /tracks/external/{source}/{externalId}/stream replace the
YouTube-only equivalents.
- POST /playlists/{id}/tracks replaces the separate
.../youtube-tracks endpoint, accepting an optional Source/ExternalId
pair alongside TrackId.
- AlbumSearchItemResponse/AlbumsSearchResponse follow the same
discriminated-union + trailing-HasNextPage-field pattern already
used for track search, so HasNextPage stays a required field in the
generated OpenAPI schema.
- Frontend routes renamed accordingly (/albums/youtube/[albumId] ->
/albums/external/[source]/[externalId], etc.) with a single
/api/thumbnail proxy replacing /api/youtube/thumbnail.
Musify.Api.Endpoints.YouTubeEndpoints and the standalone
SearchYouTubeAlbums query are removed as a result.
GET /tracks now merges the local catalog page with a live YouTube Music
search (deduplicated against tracks already provisioned locally) whenever a
name filter is given, appending the YouTube hits after the local matches and
carrying a continuation token for further pages. Each item is tagged with its
source via the new TrackSearchItemResponse/TracksSearchResponse shapes,
wrapping the existing TrackApplicationResponse or a raw YouTubeSongResult so
neither type had to change.
GET /youtube/search is removed along with its now-unused handler; the
web-player's explore page, its /api/tracks proxy, and the YouTube filler
helper are updated to call the combined endpoint instead of hitting the two
separately.
Admin