feat(immersive): create unified ImmersivePlayer component

New component architecture:
- ImmersivePlayer.svelte: Main container with tab system
- ImmersiveHeader.svelte: Tabs (lyrics/credits/suggestions/visualizer)
- ImmersiveControls.svelte: Bottom bar with all playback controls
- ImmersiveArtwork.svelte: Album art with floating/vinyl variants
- ImmersiveBackground.svelte: Optimized blur background (from Phase 1)

Panel components:
- LyricsPanel: Wrapper for existing LyricsLines
- CreditsPanel: Placeholder (Phase 3)
- SuggestionsPanel: Placeholder (Phase 4)
- VisualizerPanel: Placeholder (Phase 5)

Shared components:
- ProgressBar: Reusable seek bar with keyboard support
- VolumeSlider: Reusable volume control

Features:
- Tab-based navigation (L/C/S/V keyboard shortcuts)
- Auto-hide UI after 4 seconds of inactivity
- Full keyboard control (Space, Arrows, Escape)
- Responsive layout (desktop/tablet/mobile)
- Accessibility: ARIA roles, focus management

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

@@ -0,0 +1,58 @@
+<script lang="ts">
+  import { t } from '$lib/i18n';
+
+  interface Props {
+    trackId?: number;
+    artistId?: number;
+  }
+
+  let { trackId, artistId }: Props = $props();
+
+  // TODO: Implement suggestions fetching in Phase 4
+  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>
+    <span class="placeholder-hint">Artist Radio, Track Radio, Similar Tracks...</span>
+  </div>
+</div>
+
+<style>
+  .suggestions-panel {
+    flex: 1;
+    min-height: 0;
+    display: flex;
+    flex-direction: column;
+    overflow-y: auto;
+    padding: 24px;
+  }
+
+  .placeholder {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    gap: 12px;
+    height: 100%;
+    min-height: 200px;
+    color: var(--alpha-40, rgba(255, 255, 255, 0.4));
+  }
+
+  .placeholder-icon {
+    font-size: 32px;
+    opacity: 0.5;
+  }
+
+  .placeholder-text {
+    font-size: 16px;
+    font-weight: 500;
+  }
+
+  .placeholder-hint {
+    font-size: 13px;
+    color: var(--alpha-30, rgba(255, 255, 255, 0.3));
+  }
+</style>