perf: inline SVGs, memoize grid slices, batch store notifications

- Replace wa-icon shadow DOM with inline SVG in queue-panel (xmark)
  and album-dropdown (fav icons) to eliminate per-item shadow roots
- Memoize getBeforeEntries/getAfterEntries in cover-grid to prevent
  .slice() creating new array refs that trigger virtualizer relayout
- Remove transition: scale and border-radius from album cards to
  avoid per-frame repaints and anti-aliased path clipping
- Add queueMicrotask batching to player-store and favorites-store
  notify() to coalesce rapid-fire updates into single renders

frontend/src/store/favorites-store.ts

@@ -34,6 +34,7 @@ class FavoritesStore {
     private pinDefault = true;
     private favoritedPaths = new Set<string>();
     private subscribers = new Set<Subscriber>();
+    private notifyScheduled = false;
     private loading = false;
 
     constructor() {
@@ -232,7 +233,14 @@ class FavoritesStore {
     }
 
     private notify(): void {
-        this.subscribers.forEach((cb) => cb());
+        if (this.notifyScheduled) return;
+        this.notifyScheduled = true;
+        queueMicrotask(() => {
+            this.notifyScheduled = false;
+            for (const cb of this.subscribers) {
+                cb();
+            }
+        });
     }
 
     // ===============================================================

frontend/src/store/player-store.ts

@@ -41,6 +41,7 @@ class PlayerStore {
   };
 
   private subscribers = new Set<Subscriber>();
+  private notifyScheduled = false;
 
   constructor() {
     this.initializeEventListeners();
@@ -115,7 +116,14 @@ class PlayerStore {
   }
 
   private notify(): void {
-    this.subscribers.forEach((callback) => callback());
+    if (this.notifyScheduled) return;
+    this.notifyScheduled = true;
+    queueMicrotask(() => {
+      this.notifyScheduled = false;
+      for (const sub of this.subscribers) {
+        sub();
+      }
+    });
   }
 }