feat: add similar songs functionality in agents, and Instant Mix (song-based) to UI (#4919)

* refactor: rename ArtistRadio to SimilarSongs for clarity and consistency

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: implement GetSimilarSongsByTrack and related functionality for song similarity retrieval

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: enhance GetSimilarSongsByTrack to include artist and album details and update tests

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: enhance song matching by implementing title and artist filtering in loadTracksByTitleAndArtist

Signed-off-by: Deluan <deluan@navidrome.org>

* test: add unit tests for song matching functionality in provider

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: extract song matching functionality into its own file

Signed-off-by: Deluan <deluan@navidrome.org>

* docs: clarify similarSongsFallback function description in provider.go

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: initialize result slice for songs with capacity based on response length

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: simplify agent method calls for retrieving images and similar songs

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: simplify agent method calls for retrieving images and similar songs

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: remove outdated comments in GetSimilarSongs methods

Signed-off-by: Deluan <deluan@navidrome.org>

* fix: use composite key for song matches to handle duplicates by title and artist

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: consolidate expectations setup for similar songs tests

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: add instant mix action to song context menu and update translations

Signed-off-by: Deluan <deluan@navidrome.org>

* fix(provider): handle unknown entity types in GetSimilarSongs

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: move playSimilar action to playbackActions and streamline song processing

Signed-off-by: Deluan <deluan@navidrome.org>

* format

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: enhance instant mix functionality with loading notification and shuffle option

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: implement fuzzy matching for similar songs based on configurable threshold

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: implement track matching with multiple specificity levels

Signed-off-by: Deluan <deluan@navidrome.org>

* refactor: enhance track matching by implementing unified scoring with specificity levels

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: enhance deezer top tracks result with album

Signed-off-by: Deluan <deluan@navidrome.org>

* feat: enhance track matching with fuzzy album similarity for improved scoring

Signed-off-by: Deluan <deluan@navidrome.org>

* docs: document multi-phase song matching algorithm with detailed scoring and prioritization

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>

server/subsonic/browsing.go

@@ -354,7 +354,7 @@ func (api *Router) GetSimilarSongs(r *http.Request) (*responses.Subsonic, error)
 	}
 	count := p.IntOr("count", 50)
 
-	songs, err := api.provider.ArtistRadio(ctx, id, count)
+	songs, err := api.provider.SimilarSongs(ctx, id, count)
 	if err != nil {
 		return nil, err
 	}