Add v2 Game Boy sound engine (isolated from v1)

- Authentic DMG-CPU sound chip implementation:
  - 4 Pulse channels with duty cycle control (12.5%, 25%, 50%, 75%)
  - 2 Wave channels with 4-bit wavetables
  - 2 Noise channels with LFSR (7-bit and 15-bit modes)

- GameBoy Colorizer effect chain:
  - Low-pass filter (natural GB rolloff)
  - Bit-crushing (4-bit DAC simulation)
  - Sample rate reduction
  - Saturation and high-pass filter
  - Presets: DMG, GBC, GBA, Clean

- Intelligent MIDI processing:
  - Track analysis and role detection (bass, lead, drums, etc.)
  - Automatic channel mapping to GB channels
  - Chord arpeggiator for polyphony handling
  - GameBoy Arranger for fuller sound

- BitMidi search integration
- Completely isolated from v1 (no changes to src/)

src-v2/types/index.ts

@@ -0,0 +1,151 @@
+/**
+ * Wario Synth v2 Type Definitions
+ * 
+ * Types specific to the Game Boy-authentic synthesis engine.
+ */
+
+import type { DutyIndex } from '../audio/synthesis/DutyCycle';
+import type { LFSRMode } from '../audio/synthesis/LFSR';
+import type { WavePreset, WaveVolume } from '../audio/synthesis/WaveTable';
+
+/**
+ * Channel identifiers for the 8-channel "Super Game Boy" setup
+ */
+export type PulseChannelId = 'p1' | 'p2' | 'p3' | 'p4';
+export type WaveChannelId = 'w1' | 'w2';
+export type NoiseChannelId = 'n1' | 'n2';
+export type ChannelId = PulseChannelId | WaveChannelId | NoiseChannelId;
+
+/**
+ * A note scheduled to play on a specific channel
+ */
+export interface ChannelNote {
+  channel: ChannelId;
+  midiNote: number;
+  startTime: number;      // In seconds from playback start
+  duration: number;       // In seconds
+  velocity: number;       // 0-127
+}
+
+/**
+ * Pulse channel configuration
+ */
+export interface PulseChannelConfig {
+  id: PulseChannelId;
+  hasSweep: boolean;
+  defaultDuty: DutyIndex;
+  role: 'lead' | 'fx' | 'harmony' | 'arp';
+}
+
+/**
+ * Wave channel configuration
+ */
+export interface WaveChannelConfig {
+  id: WaveChannelId;
+  preset: WavePreset;
+  role: 'bass' | 'texture';
+}
+
+/**
+ * Noise channel configuration
+ */
+export interface NoiseChannelConfig {
+  id: NoiseChannelId;
+  mode: LFSRMode;
+  role: 'percussion' | 'hihats';
+}
+
+/**
+ * Track role for MIDI analysis
+ */
+export type TrackRole = 'drums' | 'bass' | 'lead' | 'harmony' | 'pad' | 'fx';
+
+/**
+ * Analysis result for a single MIDI track
+ */
+export interface TrackAnalysis {
+  trackIndex: number;
+  channel: number;                    // MIDI channel (0-15, 9 = drums)
+  isDrums: boolean;
+  isPercussive: boolean;
+  noteRange: {
+    min: number;
+    max: number;
+    avg: number;
+  };
+  noteDensity: number;                // Notes per second
+  complexity: number;                 // 0-1 score
+  hasChords: boolean;
+  avgVelocity: number;
+  avgDuration: number;
+  noteCount: number;
+  role: TrackRole;
+  priority: number;                   // Higher = more important
+}
+
+/**
+ * Assignment of a MIDI track to a GB channel
+ */
+export interface ChannelAssignment {
+  trackIndex: number;
+  channelId: ChannelId;
+  shouldArpeggiate: boolean;
+  dutyCycle?: DutyIndex;              // For pulse channels
+  wavePreset?: WavePreset;            // For wave channels
+  noiseMode?: LFSRMode;               // For noise channels
+}
+
+/**
+ * Note format for arpeggiator processing
+ */
+export interface ArpNote {
+  midiNote: number;
+  time: number;
+  duration: number;
+  velocity: number;
+}
+
+/**
+ * Grouped chord for arpeggiator
+ */
+export interface ArpChord {
+  startTime: number;
+  notes: ArpNote[];
+}
+
+/**
+ * v2 Engine configuration
+ */
+export interface V2Config {
+  masterVolume: number;               // 0-1
+  lookaheadTime: number;              // Scheduling lookahead in seconds
+  scheduleInterval: number;           // Scheduler interval in ms
+}
+
+/**
+ * Default configuration values
+ */
+export const DEFAULT_V2_CONFIG: V2Config = {
+  masterVolume: 0.7,
+  lookaheadTime: 0.1,
+  scheduleInterval: 25,
+};
+
+/**
+ * Channel state for APU
+ */
+export interface ChannelState {
+  id: ChannelId;
+  isBusy: boolean;
+  busyUntil: number;                  // AudioContext time when channel becomes free
+  currentGain: number;
+}
+
+/**
+ * Playback result info
+ */
+export interface PlaybackInfo {
+  duration: number;
+  assignments: ChannelAssignment[];
+  noteCount: number;
+}