feat(visualizer): add multiple visualizers with mouse tracking and beat response

- Add BaseVisualizer class for shared visualizer logic
- Add Helix visualizer (DNA helix with rungs, beat compression/bounce)
- Add Tunnel visualizer (ring tunnel with depth parallax)
- Refactor SphereVisualizer to extend BaseVisualizer
- Add mouse tracking to all visualizers (canvas-relative, centered)
- Add visualizer switching via logo click (persisted to localStorage)
- Add beat-responsive bouncing and compression effects

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

layouts/_default/baseof.html

@@ -64,6 +64,18 @@
 
       // Player UI component
       Alpine.data('playerUI', () => ({
+        visualizerName: 'Sphere',
+
+        init() {
+          // Get initial visualizer name
+          this.$nextTick(() => {
+            const viz = window.__pivoine?.visualizer;
+            if (viz) {
+              this.visualizerName = viz.getCurrentName() || 'Sphere';
+            }
+          });
+        },
+
         togglePlay() {
           window.__pivoine?.audioManager?.toggle();
         },
@@ -85,6 +97,12 @@
             this.setVolume(this._previousVolume || 0.8);
           }
         },
+        cycleVisualizer() {
+          const viz = window.__pivoine?.visualizer;
+          if (viz) {
+            this.visualizerName = viz.nextVisualizer();
+          }
+        },
         formatTime(seconds) {
           if (!seconds || isNaN(seconds)) return '0:00';
           const mins = Math.floor(seconds / 60);