feat: add advanced audio effects and improve UI

Phase 6.5 Advanced Effects:
- Add Pitch Shifter with semitones and cents adjustment
- Add Time Stretch with pitch preservation using overlap-add
- Add Distortion with soft/hard/tube types and tone control
- Add Bitcrusher with bit depth and sample rate reduction
- Add AdvancedParameterDialog with real-time waveform visualization
- Add 4 professional presets per effect type

Improvements:
- Fix undefined parameter errors by adding nullish coalescing operators
- Add global custom scrollbar styling with color-mix transparency
- Add custom-scrollbar utility class for side panel
- Improve theme-aware scrollbar appearance in light/dark modes
- Fix parameter initialization when switching effect types

Integration:
- All advanced effects support undo/redo via EffectCommand
- Effects accessible via command palette and side panel
- Selection-based processing support
- Toast notifications for all effects

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

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

lib/audio/effects/normalize.ts

@@ -0,0 +1,132 @@
+/**
+ * Normalization effects
+ */
+
+import { getAudioContext } from '../context';
+
+/**
+ * Normalize audio to peak amplitude
+ * @param buffer - Source audio buffer
+ * @param targetPeak - Target peak amplitude (0.0 to 1.0, default 1.0)
+ * @returns New audio buffer with normalized audio
+ */
+export function normalizePeak(buffer: AudioBuffer, targetPeak: number = 1.0): AudioBuffer {
+  const audioContext = getAudioContext();
+
+  // Find the absolute peak across all channels
+  let maxPeak = 0;
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const channelData = buffer.getChannelData(channel);
+    for (let i = 0; i < buffer.length; i++) {
+      const abs = Math.abs(channelData[i]);
+      if (abs > maxPeak) {
+        maxPeak = abs;
+      }
+    }
+  }
+
+  // Calculate gain factor
+  const gainFactor = maxPeak > 0 ? targetPeak / maxPeak : 1.0;
+
+  // Create output buffer and apply gain
+  const outputBuffer = audioContext.createBuffer(
+    buffer.numberOfChannels,
+    buffer.length,
+    buffer.sampleRate
+  );
+
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const inputData = buffer.getChannelData(channel);
+    const outputData = outputBuffer.getChannelData(channel);
+
+    for (let i = 0; i < buffer.length; i++) {
+      outputData[i] = inputData[i] * gainFactor;
+    }
+  }
+
+  return outputBuffer;
+}
+
+/**
+ * Normalize audio to RMS (loudness)
+ * @param buffer - Source audio buffer
+ * @param targetRMS - Target RMS level (0.0 to 1.0, default 0.5)
+ * @returns New audio buffer with normalized audio
+ */
+export function normalizeRMS(buffer: AudioBuffer, targetRMS: number = 0.5): AudioBuffer {
+  const audioContext = getAudioContext();
+
+  // Calculate RMS across all channels
+  let sumSquares = 0;
+  let totalSamples = 0;
+
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const channelData = buffer.getChannelData(channel);
+    for (let i = 0; i < buffer.length; i++) {
+      sumSquares += channelData[i] * channelData[i];
+      totalSamples++;
+    }
+  }
+
+  const currentRMS = Math.sqrt(sumSquares / totalSamples);
+  const gainFactor = currentRMS > 0 ? targetRMS / currentRMS : 1.0;
+
+  // Create output buffer and apply gain
+  const outputBuffer = audioContext.createBuffer(
+    buffer.numberOfChannels,
+    buffer.length,
+    buffer.sampleRate
+  );
+
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const inputData = buffer.getChannelData(channel);
+    const outputData = outputBuffer.getChannelData(channel);
+
+    for (let i = 0; i < buffer.length; i++) {
+      outputData[i] = inputData[i] * gainFactor;
+      // Clamp to prevent distortion
+      outputData[i] = Math.max(-1, Math.min(1, outputData[i]));
+    }
+  }
+
+  return outputBuffer;
+}
+
+/**
+ * Get peak amplitude of audio buffer
+ * @param buffer - Audio buffer
+ * @returns Peak amplitude (0.0 to 1.0)
+ */
+export function getPeakAmplitude(buffer: AudioBuffer): number {
+  let maxPeak = 0;
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const channelData = buffer.getChannelData(channel);
+    for (let i = 0; i < buffer.length; i++) {
+      const abs = Math.abs(channelData[i]);
+      if (abs > maxPeak) {
+        maxPeak = abs;
+      }
+    }
+  }
+  return maxPeak;
+}
+
+/**
+ * Get RMS amplitude of audio buffer
+ * @param buffer - Audio buffer
+ * @returns RMS amplitude
+ */
+export function getRMSAmplitude(buffer: AudioBuffer): number {
+  let sumSquares = 0;
+  let totalSamples = 0;
+
+  for (let channel = 0; channel < buffer.numberOfChannels; channel++) {
+    const channelData = buffer.getChannelData(channel);
+    for (let i = 0; i < buffer.length; i++) {
+      sumSquares += channelData[i] * channelData[i];
+      totalSamples++;
+    }
+  }
+
+  return Math.sqrt(sumSquares / totalSamples);
+}