feat: implement medium effort features - markers, web workers, and bezier automation

Implemented three major medium effort features to enhance the audio editor:

**1. Region Markers System**
- Add marker type definitions supporting point markers and regions
- Create useMarkers hook for marker state management
- Build MarkerTimeline component for visual marker display
- Create MarkerDialog component for adding/editing markers
- Add keyboard shortcuts: M (add marker), Shift+M (next), Shift+Ctrl+M (previous)
- Support marker navigation, editing, and deletion

**2. Web Worker for Computations**
- Create audio worker for offloading heavy computations
- Implement worker functions: generatePeaks, generateMinMaxPeaks, normalizePeaks, analyzeAudio, findPeak
- Build useAudioWorker hook for easy worker integration
- Integrate worker into Waveform component with peak caching
- Significantly improve UI responsiveness during waveform generation

**3. Bezier Curve Automation**
- Enhance interpolateAutomationValue to support Bezier curves
- Implement cubic Bezier interpolation with control handles
- Add createSmoothHandles for auto-smooth curve generation
- Add generateBezierCurvePoints for smooth curve rendering
- Support bezier alongside existing linear and step curves

All features are type-safe and integrate seamlessly with the existing codebase.

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

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

types/marker.ts

@@ -0,0 +1,29 @@
+/**
+ * Region marker type definitions
+ * Markers help navigate and organize the timeline
+ */
+
+/**
+ * Marker types
+ * - point: A single point in time (like a cue point)
+ * - region: A time range with start and end
+ */
+export type MarkerType = 'point' | 'region';
+
+/**
+ * Single marker or region
+ */
+export interface Marker {
+  id: string;
+  name: string;
+  type: MarkerType;
+  time: number; // Start time in seconds
+  endTime?: number; // End time for regions (undefined for point markers)
+  color?: string; // Optional color for visual distinction
+  description?: string; // Optional description/notes
+}
+
+/**
+ * Helper type for creating new markers
+ */
+export type CreateMarkerInput = Omit<Marker, 'id'>;