fix: only swap YTM thumbnail for music videos, not audio tracks

[sang765]

The rememberThumbnailSwapState composable was attempting to load YT i.ytimg.com thumbnails for every item with a non-null videoId, regardless of whether it was a music video or an audio track. This caused "Music" type items (1:1 YTM art) to silently get their thumbnail swapped to YT lower-quality video thumbnails.

The static isMusicVideo flag from musicVideoType (OMV/UGC) misses some video items. This fix adds a runtime check using Media3 Player.getTracks() to detect actual video tracks at playback time.

Changes:

• Added hasVideoTracks StateFlow to PlayerConnection, initialized from player.tracks and updated on onTracksChanged
• Updated rememberThumbnailSwapState to accept hasVideoTracks: Boolean and use isMusicVideo || hasVideoTracks
• Updated all 9 call sites to pass hasVideoTracks from playerConnection

The shouldAttemptYT flag now requires videoId != null && !lowDataMode && (isMusicVideo || hasVideoTracks) — the runtime thumbnail swap fires only when the item is statically flagged as a music video OR the Media3 player reports active video tracks.