Add real-time voice effects for outgoing audio

Implements 7 voice effects that can be cycled through with F12:
- None (default)
- Echo: Single repeating delay with feedback (250ms)
- Reverb: Multiple short delays without feedback
- High Pitch: Chipmunk voice using cubic interpolation
- Low Pitch: Deep voice effect
- Robot: Ring modulation for robotic sound
- Chorus: Layered voices with pitch variations

The effects are applied after noise suppression and AGC in the audio
pipeline. Selected effect is persisted to config file. Includes
comprehensive documentation in README.

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

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

ui.go

@@ -99,7 +99,7 @@ func (b *Barnard) OnNoiseSuppressionToggle(ui *uiterm.Ui, key uiterm.Key) {
     enabled := !b.UserConfig.GetNoiseSuppressionEnabled()
     b.UserConfig.SetNoiseSuppressionEnabled(enabled)
     b.NoiseSuppressor.SetEnabled(enabled)
-    
+
     if enabled {
         b.UpdateGeneralStatus("Noise suppression: ON", false)
     } else {
@@ -107,6 +107,12 @@ func (b *Barnard) OnNoiseSuppressionToggle(ui *uiterm.Ui, key uiterm.Key) {
     }
 }
 
+func (b *Barnard) OnVoiceEffectCycle(ui *uiterm.Ui, key uiterm.Key) {
+    effect := b.VoiceEffects.CycleEffect()
+    b.UserConfig.SetVoiceEffect(int(effect))
+    b.UpdateGeneralStatus(fmt.Sprintf("Voice effect: %s", effect.String()), false)
+}
+
 
 func (b *Barnard) UpdateGeneralStatus(text string, notice bool) {
     if notice {
@@ -323,6 +329,7 @@ func (b *Barnard) OnUiInitialize(ui *uiterm.Ui) {
     b.Ui.AddKeyListener(b.OnVoiceToggle, b.Hotkeys.Talk)
     b.Ui.AddKeyListener(b.OnTimestampToggle, b.Hotkeys.ToggleTimestamps)
     b.Ui.AddKeyListener(b.OnNoiseSuppressionToggle, b.Hotkeys.NoiseSuppressionToggle)
+    b.Ui.AddKeyListener(b.OnVoiceEffectCycle, b.Hotkeys.CycleVoiceEffect)
     b.Ui.AddKeyListener(b.OnQuitPress, b.Hotkeys.Exit)
     b.Ui.AddKeyListener(b.OnScrollOutputUp, b.Hotkeys.ScrollUp)
     b.Ui.AddKeyListener(b.OnScrollOutputDown, b.Hotkeys.ScrollDown)