chore(web/lint): clear svelte-check warnings + fix QueueDrawer test query

CI svelte-check was blocking on:

- 1 ERROR I introduced in the previous cleanup: QueueDrawer.test.ts
  passed { hidden: true } to getByLabelText, but that option only
  exists on getByRole. Fixed by switching to a direct
  document.querySelector for the aria-hidden assertion.

- 13 WARNINGS pre-existing in the codebase from M7 #352/#372/#349
  era, never surfaced because earlier CI runs failed before reaching
  type-check. Now that CI gets that far, they accumulate. Cleared:

  - FlagPopover, RemoveTrackPopover, AddToPlaylistMenu, TrackMenu:
    interactive role divs gain tabindex="-1" + onkeydown that stops
    propagation and closes on Escape (functional, not just warning-
    suppression).

  - FlagPopover state-from-props: $state(untrack(() => prop ?? default))
    for explicit initial-snapshot semantics; const isUpdate switched
    to $derived so it reacts to prop changes.

  - PlaylistTrackRow drag-div: role="listitem" added.

  - playlists/+page.svelte: autofocus replaced with bind:this + $effect.

web/src/routes/playlists/+page.svelte

@@ -16,6 +16,11 @@
   let newName = $state('');
   let creatingBusy = $state(false);
   let createError = $state<string | null>(null);
+  let inputEl: HTMLInputElement | undefined = $state();
+
+  $effect(() => {
+    inputEl?.focus();
+  });
 
   async function submitCreate() {
     if (!newName.trim()) {
@@ -59,9 +64,9 @@
         Name
         <input
           type="text"
+          bind:this={inputEl}
           bind:value={newName}
           placeholder="Saturday morning"
-          autofocus
           class="mt-1 w-full rounded border border-border bg-background px-3 py-1.5 text-sm text-text-primary"
           onkeydown={(e) => { if (e.key === 'Enter') submitCreate(); if (e.key === 'Escape') creating = false; }}
         />