feat(radio): replace robot TTS with Piper Neural voices & add instant voice preview

- Integrate local Piper ONNX neural TTS engine (Dmitri, Irina, Denis, Ruslan)
- Add GET /api/radio/preview-voice endpoint with cached pre-rendered samples
- Add '▶ Прослушать голос' button in Web UI for 1-click preview before generating
- Add automated filter to strip LLM refusals and fall back to clean radio phrasing

app/static/app.js

@@ -501,6 +501,7 @@ document.addEventListener("DOMContentLoaded", () => {
   // --- AI Radio Host Controller (Phase 3) ---
   const radioGenerateBtn = document.getElementById("radioGenerateBtn");
   const radioVoiceSelect = document.getElementById("radioVoiceSelect");
+  const radioVoicePreviewBtn = document.getElementById("radioVoicePreviewBtn");
   const radioStatusLabel = document.getElementById("radioStatusLabel");
   const radioClipsCountLabel = document.getElementById("radioClipsCountLabel");
   const radioSegmentsContainer = document.getElementById("radioSegmentsContainer");
@@ -508,10 +509,29 @@ document.addEventListener("DOMContentLoaded", () => {
 
   fetchRadioStatus();
 
+  // Voice sample preview playback
+  if (radioVoicePreviewBtn) {
+    radioVoicePreviewBtn.addEventListener("click", () => {
+      const selectedVoice = radioVoiceSelect ? radioVoiceSelect.value : "ru_RU-dmitri-medium";
+      const audioUrl = `api/radio/preview-voice?voice=${encodeURIComponent(selectedVoice)}`;
+      const selectedOption = (radioVoiceSelect && radioVoiceSelect.options[radioVoiceSelect.selectedIndex]) 
+        ? radioVoiceSelect.options[radioVoiceSelect.selectedIndex].text 
+        : "Голос ведущего";
+      playPreviewTrack(
+        audioUrl,
+        `Сэмпл: ${selectedOption}`,
+        "AI Радио (Предпрослушивание)",
+        "",
+        "",
+        audioUrl
+      );
+    });
+  }
+
   if (radioGenerateBtn) {
     radioGenerateBtn.addEventListener("click", async () => {
       radioGenerateBtn.disabled = true;
-      const voice = radioVoiceSelect ? radioVoiceSelect.value : "ru-RU-DmitryNeural";
+      const voice = radioVoiceSelect ? radioVoiceSelect.value : "ru_RU-dmitri-medium";
       if (radioStatusLabel) {
         radioStatusLabel.textContent = "🎙️ Ведущий пишет реплики и сводит эфир...";
         radioStatusLabel.className = "badge badge-llm";
@@ -560,6 +580,17 @@ document.addEventListener("DOMContentLoaded", () => {
       if (radioClipsCountLabel) {
         radioClipsCountLabel.textContent = `${data.speech_clips_count || 0} записей`;
       }
+
+      // Populate voice selector dynamically
+      if (radioVoiceSelect && data.available_voices && data.available_voices.length > 0) {
+        const currentVal = radioVoiceSelect.value || data.default_voice;
+        radioVoiceSelect.innerHTML = data.available_voices.map(v => `
+          <option value="${escapeHtml(v.id)}" ${v.id === currentVal ? "selected" : ""}>
+            🎙️ ${escapeHtml(v.name)}
+          </option>
+        `).join("");
+      }
+
       if (radioStatusLabel) {
         if (data.playlist_ready && data.speech_clips_count > 0) {
           radioStatusLabel.textContent = "🟢 Эфир в ротации";