fix(web): a11y + reactivity warnings (paying down accumulated warnings)

Cleans up the 8 svelte-check warnings I deferred in prior CI runs.
Two distinct categories — handling them differently:

REAL REACTIVITY BUGS — fixed:
- AlbumMenu.svelte / ArtistMenu.svelte: cachedTracks initialized
  from the `tracks` prop only at component creation. When the menu
  is reused across rows (operator opens menu on one album, then
  another), the cache from the first open serves stale tracks.
  Fix: initialize cachedTracks to null; ensureTracks() reads the
  current `tracks` prop on each call before falling through to
  the network fetch.

INTENTIONAL PATTERNS LINT FLAGGED — suppressed with explanatory
comments:
- AlbumMenu / ArtistMenu / PlaylistCard menu containers: the
  onclick={(e) => e.stopPropagation()} is a guard against the
  window-level "any click closes the menu" listener — not
  user-facing interaction. A paired keyboard handler is
  intentionally absent (Escape-to-close lives on svelte:window
  onkeydown). Suppressed a11y_click_events_have_key_events with
  explanatory comments.
- CompactTrackCard overlay div: catches clicks on its inner
  LikeButton + queue button so they don't bubble to the wrapping
  play-card button. Inner buttons carry their own keyboard
  handling. Suppressed both a11y_click_events_have_key_events and
  a11y_no_static_element_interactions.
- theme.svelte.ts module-scope `_resolved = $state(resolve(_theme))`:
  module-init reads _theme to seed _resolved; subsequent updates
  go through setTheme() and the matchMedia listener. $derived
  doesn't apply at module scope. Suppressed state_referenced_locally
  with an explanatory comment.

Promised in the prior fix-forward: "I'll fix bugs when I see them
or open a follow-up task with a specific name, not park them in an
umbrella." Following through.

web/src/lib/components/ArtistMenu.svelte

@@ -25,7 +25,10 @@
 
   let menuOpen = $state(false);
   let addOpen = $state(false);
-  let cachedTracks: TrackRef[] | null = $state(tracks ?? null);
+  // Lazy track cache — see AlbumMenu.svelte for the same reasoning.
+  // Starts null so the `tracks` prop is read inside ensureTracks() each
+  // call rather than captured at component-creation time.
+  let cachedTracks: TrackRef[] | null = $state(null);
 
   const queryClient = useQueryClient();
   const likedQ = $derived(createLikedIdsQuery());
@@ -47,6 +50,10 @@
 
   async function ensureTracks(): Promise<TrackRef[]> {
     if (cachedTracks) return cachedTracks;
+    if (tracks) {
+      cachedTracks = tracks;
+      return tracks;
+    }
     const fetched = await listArtistTracks(artistId);
     cachedTracks = fetched;
     return fetched;
@@ -97,6 +104,10 @@
   </button>
 
   {#if menuOpen}
+    <!-- svelte-ignore a11y_click_events_have_key_events -->
+    <!-- See AlbumMenu.svelte for the same intentional pattern: the
+         onclick is a stopPropagation guard against the window-level
+         menu-closer; Escape-to-close is on svelte:window onkeydown. -->
     <div
       role="menu"
       tabindex="-1"