fix(web/m7-364): TrackRef field shape + seek-on-restore + drawer inert

CI svelte-check failed on 5 type errors caused by the slice using
duration_ms/album_name fields that don't exist on TrackRef (the real
shape uses duration_sec + album_id/album_title). Fixed across
QueueDrawer, QueueDrawer.test, QueueTrackRow.test, persisted.test,
and the inline `state.current = null` in PlayerBar.test (TrackRef |
undefined, not | null).

Final whole-slice review concerns also rolled in:

- C1 (Critical): persisted position was restored to UI but never
  seeked into the audio element — first timeupdate snapped _position
  back to 0. Added a one-shot _pendingRestorePosition module ref +
  consumePendingRestorePosition() export; layout's loadedmetadata
  handler now seeks once on restore.

- I1 (Important): throttled-write effect now wraps _queue / _index
  reads in untrack so the dependency tracking matches the design
  intent. Position remains the only tracked dep.

- I4 (Important): drawer gets inert={!queueDrawerOpen} so its inner
  buttons drop out of tab order when closed (aria-hidden alone
  doesn't do that). Removed redundant role="complementary" from
  <aside> (implied by the element). New test asserts inert binding.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/lib/components/QueueDrawer.svelte

@@ -3,10 +3,8 @@
   import { player, closeQueueDrawer } from '$lib/player/store.svelte';
   import QueueTrackRow from './QueueTrackRow.svelte';
 
-  function totalDurationLabel(tracks: { duration_ms: number }[]): string {
-    const totalSec = Math.floor(
-      tracks.reduce((s, tr) => s + (tr.duration_ms ?? 0), 0) / 1000
-    );
+  function totalDurationLabel(tracks: { duration_sec: number }[]): string {
+    const totalSec = tracks.reduce((s, tr) => s + (tr.duration_sec ?? 0), 0);
     const m = Math.floor(totalSec / 60);
     const h = Math.floor(m / 60);
     return h > 0 ? `${h}h ${m % 60}m` : `${m} min`;
@@ -23,9 +21,9 @@
 {/if}
 
 <aside
-  role="complementary"
   aria-label="Playback queue"
   aria-hidden={!player.queueDrawerOpen}
+  inert={!player.queueDrawerOpen}
   class="fixed top-0 right-0 h-full w-full sm:w-96 bg-surface z-50
          transition-transform duration-200 flex flex-col
          {player.queueDrawerOpen ? 'translate-x-0' : 'translate-x-full'}"