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.svelte

@@ -25,6 +25,9 @@
   } = $props();
 
   const track = $derived(tracks[index]);
+  // #5418: the file is gone. The row stays, greyed, so an album still reads
+  // in order, but there is nothing to play, like or queue.
+  const missing = $derived(!!track.unavailable);
 
   const isSelected = $derived(selection.isSelected(track.id));
   const selectMode = $derived(selection.active);
@@ -61,9 +64,13 @@
   title={track.title}
   {subtitle}
   durationSec={track.duration_sec}
-  {track}
+  track={missing ? null : track}
   ariaLabel={track.title}
+  rowTitle={missing
+    ? 'This track’s file is missing from the library, so it can’t be played. It returns automatically if the file comes back.'
+    : undefined}
   {isSelected}
+  disabled={missing}
   onActivate={activate}
 >
   {#snippet lead()}
@@ -88,4 +95,10 @@
       <Check size={14} strokeWidth={2} />
     </button>
   {/snippet}
+
+  {#snippet note()}
+    {#if missing}
+      <span class="text-error-fg"> · File missing</span>
+    {/if}
+  {/snippet}
 </TrackListRow>

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 } });