polish(immersive): improve panel styling and add canvas visualizer

- Replace emoji icons with Lucide icons in placeholder panels
- Add styled "Coming Soon" badges
- Create animated canvas visualizer (reacts to isPlaying state)
- Visualizer shows frequency bars with smooth animation

src/lib/components/immersive/panels/SuggestionsPanel.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { t } from '$lib/i18n';
+  import { Radio } from 'lucide-svelte';
 
   interface Props {
     trackId?: number;
@@ -8,15 +8,18 @@
 
   let { trackId, artistId }: Props = $props();
 
-  // TODO: Implement suggestions fetching in Phase 4
+  // TODO: Implement suggestions - Artist Radio, Track Radio, Similar Tracks
   let isLoading = $state(false);
 </script>
 
 <div class="suggestions-panel">
   <div class="placeholder">
-    <span class="placeholder-icon">📻</span>
-    <span class="placeholder-text">{$t('player.suggestionsComingSoon') || 'Suggestions coming soon'}</span>
+    <div class="placeholder-icon">
+      <Radio size={40} strokeWidth={1.5} />
+    </div>
+    <span class="placeholder-text">Suggestions</span>
     <span class="placeholder-hint">Artist Radio, Track Radio, Similar Tracks...</span>
+    <span class="coming-soon">Coming Soon</span>
   </div>
 </div>
 
@@ -35,24 +38,36 @@
     flex-direction: column;
     align-items: center;
     justify-content: center;
-    gap: 12px;
+    gap: 16px;
     height: 100%;
     min-height: 200px;
     color: var(--alpha-40, rgba(255, 255, 255, 0.4));
   }
 
   .placeholder-icon {
-    font-size: 32px;
-    opacity: 0.5;
+    opacity: 0.4;
   }
 
   .placeholder-text {
-    font-size: 16px;
-    font-weight: 500;
+    font-size: 18px;
+    font-weight: 600;
+    color: var(--alpha-50, rgba(255, 255, 255, 0.5));
   }
 
   .placeholder-hint {
     font-size: 13px;
     color: var(--alpha-30, rgba(255, 255, 255, 0.3));
   }
+
+  .coming-soon {
+    margin-top: 8px;
+    padding: 6px 14px;
+    background: var(--alpha-10, rgba(255, 255, 255, 0.1));
+    border-radius: 20px;
+    font-size: 11px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+    color: var(--alpha-40, rgba(255, 255, 255, 0.4));
+  }
 </style>