cover the queue/shuffle invariants the QA review flagged

The shuffled-removal tests mostly removed the *current* track (a path that
was already correct) and asserted `state.item`, which `rebuildWindow` keeps
regardless of the computed cursor, so a wrong position went unnoticed. Add:

- deterministic shuffle setup (`seedShuffledQueue`, or replace + setShuffle
  + setCursor + connect) so shuffle tests assert exact behaviour instead of
  looping over random seeds;
- controller tests that assert the queue position still resolves to the
  playing track after removing a non-current track, with and without a block,
  and that undo restores the shuffled order;
- a repository property test removing every position with a block present,
  checking the play/flat bijection, the combined/contextPlay inverse, the
  block span and that no track repeats;
- a `QueueRow.isPlaying` predicate (position AND song id) extracted and
  unit-tested, and QueueViewModel tests for starting a shuffled queue at the
  top and reconciling after a shuffled removal;
- Shuffle degenerate/out-of-range/MAX_SIZE coverage.

app/src/main/kotlin/com/subtracks/ui/playback/QueueScreen.kt

@@ -80,6 +80,13 @@ data class QueueRow(
     val upNext: Boolean = false,
 )
 
+// Both must match: the position alone can transiently point at the row above while the list
+// reconciles, and the song id alone lights up a duplicate elsewhere in the queue.
+internal fun QueueRow.isPlaying(
+    currentPosition: Long?,
+    currentSongId: String?,
+): Boolean = position == currentPosition && song.song.id == currentSongId
+
 class QueueViewModel(
     private val queueRepository: QueueRepository,
     private val playbackController: PlaybackController,
@@ -436,7 +443,7 @@ fun QueueScreen(
                             ) { isDragging ->
                                 QueueRowItem(
                                     row = row,
-                                    isPlaying = row.position == currentPosition && row.song.song.id == currentSongId,
+                                    isPlaying = row.isPlaying(currentPosition, currentSongId),
                                     floating = isDragging,
                                     coverArt = coverArt,
                                     dragHandle =