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* refactor: remove outdated comments in GetSimilarSongs methods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>

ui/src/i18n/en.json

@@ -47,7 +47,8 @@
         "shuffleAll": "Shuffle All",
         "download": "Download",
         "playNext": "Play Next",
-        "info": "Get Info"
+        "info": "Get Info",
+        "instantMix": "Instant Mix"
       }
     },
     "album": {
@@ -558,6 +559,7 @@
     "transcodingEnabled": "Navidrome is currently running with %{config}, making it possible to run system commands from the transcoding settings using the web interface. We recommend to disable it for security reasons and only enable it when configuring Transcoding options.",
     "songsAddedToPlaylist": "Added 1 song to playlist |||| Added %{smart_count} songs to playlist",
     "noSimilarSongsFound": "No similar songs found",
+    "startingInstantMix": "Loading Instant Mix...",
     "noTopSongsFound": "No top songs found",
     "noPlaylistsAvailable": "None available",
     "delete_user_title": "Delete user '%{name}'",