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>

assets/js/visualizer/base-visualizer.js

@@ -0,0 +1,90 @@
+/**
+ * Base Visualizer Class
+ * Abstract base for all audio visualizers
+ */
+
+import * as THREE from 'three';
+
+export class BaseVisualizer {
+  constructor(scene) {
+    this.scene = scene;
+    this.mesh = null;
+    this.isVisible = false;
+  }
+
+  /**
+   * Initialize geometry, materials, and mesh
+   * Override in subclasses
+   */
+  init() {
+    throw new Error('init() must be implemented by subclass');
+  }
+
+  /**
+   * Update visualizer with audio data
+   * @param {Object} bands - { low, mid, high } frequency bands (0-1)
+   * @param {number} time - Animation time
+   */
+  update(bands, time) {
+    throw new Error('update() must be implemented by subclass');
+  }
+
+  /**
+   * Add visualizer to scene
+   */
+  show() {
+    if (this.mesh && !this.isVisible) {
+      this.scene.add(this.mesh);
+      this.isVisible = true;
+    }
+  }
+
+  /**
+   * Remove visualizer from scene
+   */
+  hide() {
+    if (this.mesh && this.isVisible) {
+      this.scene.remove(this.mesh);
+      this.isVisible = false;
+    }
+  }
+
+  /**
+   * Cleanup resources
+   */
+  dispose() {
+    this.hide();
+    if (this.mesh) {
+      this.mesh.geometry?.dispose();
+      if (this.mesh.material) {
+        if (Array.isArray(this.mesh.material)) {
+          this.mesh.material.forEach(m => m.dispose());
+        } else {
+          this.mesh.material.dispose();
+        }
+      }
+    }
+  }
+
+  /**
+   * Helper: Create shader material with common settings
+   */
+  createShaderMaterial(vertexShader, fragmentShader, uniforms = {}) {
+    return new THREE.ShaderMaterial({
+      vertexShader,
+      fragmentShader,
+      uniforms: {
+        uTime: { value: 0 },
+        uLow: { value: 0 },
+        uMid: { value: 0 },
+        uHigh: { value: 0 },
+        ...uniforms
+      },
+      transparent: true,
+      blending: THREE.AdditiveBlending,
+      depthWrite: false
+    });
+  }
+}
+
+export default BaseVisualizer;