feat: complete Phase 8.3 - recording settings (input gain, mono/stereo, sample rate)

Recording Settings (Phase 8.3):
- Added input gain control (0.0-2.0 with dB display)
- Real-time gain adjustment via GainNode during recording
- Mono/Stereo recording mode selection
- Sample rate matching (44.1kHz, 48kHz, 96kHz)
- Mono conversion averages all channels when enabled
- Recording settings panel shown when track is armed

Components Created:
- RecordingSettings.tsx: Settings panel with gain slider, mono/stereo toggle, sample rate buttons

Components Modified:
- useRecording hook: Added settings state and GainNode integration
- AudioEditor: Pass recording settings to TrackList
- TrackList: Forward settings to Track components
- Track: Show RecordingSettings when armed for recording

Technical Details:
- GainNode inserted between source and analyser in recording chain
- Real-time gain updates via gainNode.gain.value
- AudioContext created with target sample rate
- Mono conversion done post-recording by averaging channels
- Settings persist during recording session

Phase 8 Complete:
- ✅ Phase 8.1: Audio Input
- ✅ Phase 8.2: Recording Controls (punch/overdub)
- ✅ Phase 8.3: Recording Settings
- 📋 Phase 9: Automation (NEXT)

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

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

components/editor/AudioEditor.tsx

@@ -47,9 +47,13 @@ export function AudioEditor() {
   // Recording hook
   const {
     state: recordingState,
+    settings: recordingSettings,
     startRecording,
     stopRecording,
     requestPermission,
+    setInputGain,
+    setRecordMono,
+    setSampleRate,
   } = useRecording();
 
   // Multi-track hooks
@@ -689,6 +693,10 @@ export function AudioEditor() {
               recordingTrackId={recordingTrackId}
               recordingLevel={recordingState.inputLevel}
               trackLevels={trackLevels}
+              recordingSettings={recordingSettings}
+              onInputGainChange={setInputGain}
+              onRecordMonoChange={setRecordMono}
+              onSampleRateChange={setSampleRate}
             />
           </div>