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/components/queue-panel/queue-panel.ts

@@ -1,4 +1,4 @@
-import { LitElement, html, css, nothing, unsafeCSS } from 'lit';
+import { LitElement, html, svg, css, nothing, unsafeCSS } from 'lit';
 import { designTokens } from '../../styles/tokens.css';
 import {
     customElement,
@@ -1351,7 +1351,9 @@ export class QueuePanel
                     class="remove-button"
                     title="Remove from queue"
                 >
-                    <wa-icon name="xmark"></wa-icon>
+                    <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512" width="14" height="14">
+                        ${svg`<path fill="currentColor" d="M342.6 150.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0L192 210.7 86.6 105.4c-12.5-12.5-32.8-12.5-45.3 0s-12.5 32.8 0 45.3L146.7 256 41.4 361.4c-12.5 12.5-12.5 32.8 0 45.3s32.8 12.5 45.3 0L192 301.3 297.4 406.6c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L237.3 256 342.6 150.6z"/>`}
+                    </svg>
                 </button>
             </div>
         `;