feat: implement Phase 2 - Web Audio API engine and waveform visualization

Phase 2 Complete Features:
- Web Audio API context management with browser compatibility
- Audio file upload with drag-and-drop support
- Audio decoding for multiple formats (WAV, MP3, OGG, FLAC, AAC, M4A)
- AudioPlayer class with full playback control
- Waveform visualization using Canvas API
- Real-time waveform rendering with progress indicator
- Playback controls (play, pause, stop, seek)
- Volume control with mute/unmute
- Timeline scrubbing
- Audio file information display

Components:
- AudioEditor: Main editor container
- FileUpload: Drag-and-drop file upload component
- AudioInfo: Display audio file metadata
- Waveform: Canvas-based waveform visualization
- PlaybackControls: Transport controls with volume slider

Audio Engine:
- lib/audio/context.ts: AudioContext management
- lib/audio/decoder.ts: Audio file decoding utilities
- lib/audio/player.ts: AudioPlayer class for playback
- lib/waveform/peaks.ts: Waveform peak generation

Hooks:
- useAudioPlayer: Complete audio player state management

Types:
- types/audio.ts: TypeScript definitions for audio types

Features Working:
✓ Load audio files via drag-and-drop or file picker
✓ Display waveform with real-time progress
✓ Play/pause/stop controls
✓ Seek by clicking on waveform or using timeline slider
✓ Volume control with visual feedback
✓ Audio file metadata display (duration, sample rate, channels)
✓ Toast notifications for user feedback
✓ SSR-safe audio context initialization
✓ Dark/light theme support

Tech Stack:
- Web Audio API for playback
- Canvas API for waveform rendering
- React 19 hooks for state management
- TypeScript for type safety

Build verified and working ✓

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

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

types/audio.ts

@@ -0,0 +1,44 @@
+/**
+ * Audio type definitions for the audio editor
+ */
+
+export interface AudioFile {
+  id: string;
+  name: string;
+  size: number;
+  duration: number;
+  sampleRate: number;
+  numberOfChannels: number;
+  buffer: AudioBuffer;
+}
+
+export interface PlaybackState {
+  isPlaying: boolean;
+  isPaused: boolean;
+  currentTime: number;
+  duration: number;
+  volume: number;
+  playbackRate: number;
+}
+
+export interface WaveformData {
+  peaks: Float32Array[];
+  length: number;
+  sampleRate: number;
+  duration: number;
+}
+
+export interface Region {
+  id: string;
+  start: number;
+  end: number;
+  label?: string;
+  color?: string;
+}
+
+export interface AudioContext {
+  context: AudioContext | null;
+  buffer: AudioBuffer | null;
+  source: AudioBufferSourceNode | null;
+  gainNode: GainNode | null;
+}