v0.2: streaming playback, model params, text input

- Stream audio directly to device via BufferedWaveProvider (no temp WAVs)
- Add Noise/Speed/NoiseW sliders with live value labels
- Sliders reinit engine on MouseUp (not Scroll) to avoid locking
- Add text input field with Speak button for direct synthesis
- Test button uses text input if non-empty
- Fix sentence terminator auto-append (espeak-ng final-word drop)
- Fix UTF-8 text marshaling (piper_synthesize_start keeps text ref)
- Fix voice catalogue language column (JSON snake_case mapping)
- Use piper_default_synthesize_options for model-specific defaults
- Fix nullable warnings in designer files
- Fix unused _playing field in AudioOutput

Robovoice.App/MainForm.cs

@@ -49,6 +49,13 @@ internal sealed partial class MainForm : Form
         cmbOutput.SelectedIndexChanged += OnOutputChanged;
         cmbVoice.SelectedIndexChanged += OnVoiceChanged;
 
+        trkNoise.Scroll += OnSliderScroll;
+        trkSpeed.Scroll += OnSliderScroll;
+        trkNoiseW.Scroll += OnSliderScroll;
+        trkNoise.MouseUp += OnSliderReleased;
+        trkSpeed.MouseUp += OnSliderReleased;
+        trkNoiseW.MouseUp += OnSliderReleased;
+
         SetupTray();
 
         await InitializeEngineAsync();
@@ -124,7 +131,12 @@ internal sealed partial class MainForm : Form
         _audioOutput?.Dispose();
         _tts?.DisposeAsync().AsTask().Wait();
 
-        _tts = new LibPiperTtsEngine(modelPath, _espeakDataPath);
+        _tts = new LibPiperTtsEngine(
+            modelPath,
+            _espeakDataPath,
+            noiseScale: trkNoise.Value / 1000.0f,
+            lengthScale: trkSpeed.Value / 100.0f,
+            noiseWScale: trkNoiseW.Value / 1000.0f);
         _audioOutput = new AudioOutput();
         _sttSource = new FileSttSource();
         _orchestrator?.DisposeAsync().AsTask().Wait();
@@ -272,6 +284,21 @@ internal sealed partial class MainForm : Form
         await InitializeEngineAsync();
     }
 
+    private void OnSliderScroll(object? sender, EventArgs e)
+    {
+        lblNoiseVal.Text = $"{trkNoise.Value / 1000.0:F3}";
+        lblSpeedVal.Text = $"{trkSpeed.Value / 100.0:F2}";
+        lblNoiseWVal.Text = $"{trkNoiseW.Value / 1000.0:F3}";
+    }
+
+    private void OnSliderReleased(object? sender, MouseEventArgs e)
+    {
+        if (cmbVoice.SelectedItem is string name && VoiceCatalogue.IsVoiceInstalled(_voicesDir, name))
+        {
+            _ = InitializeEngineAsync();
+        }
+    }
+
     private void OnPttKeyChanged(object? sender, EventArgs e)
     {
         SetupHotkey();