fix(web): missing files show greyed in track lists and never enter the queue (#5418)

TrackRef gains the unavailable flag the server already sends on album
detail and search. TrackRow greys such a row with '· File missing' and
hides like, radio, add and the menu, as playlist rows already do. Every
player-store entry point (playQueue, enqueue, play next, and a refetched
mix) drops missing files; playQueue keeps the chosen track as the start.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/lib/components/TrackRow.test.ts

@@ -89,6 +89,20 @@ describe('TrackRow', () => {
     ).toBeInTheDocument();
   });
 
+  // #5418: a missing file stays in the list, greyed, with nothing to act on.
+  test('a missing file is marked, does not play, and offers no actions', async () => {
+    const withMissing = [{ ...tracks[0], unavailable: true }, tracks[1]];
+    render(TrackRow, { props: { tracks: withMissing, index: 0 } });
+    const row = screen.getByRole('button', { name: 'So What' });
+    expect(row).toHaveAttribute('aria-disabled', 'true');
+    expect(screen.getByText(/file missing/i)).toBeInTheDocument();
+    await fireEvent.click(row);
+    expect(playQueue).not.toHaveBeenCalled();
+    expect(screen.queryByRole('button', { name: /add .* to queue/i })).not.toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: /play radio/i })).not.toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: /track actions for/i })).not.toBeInTheDocument();
+  });
+
   describe('selection mode', () => {
     test('clicking the checkbox toggles selection without playing', async () => {
       render(TrackRow, { props: { tracks, index: 0 } });