feat(diagnostic): Speed-Slider im Voice-Preview-Modal (nicht persistiert)

Neue −0.1 / +0.1 Buttons im Preview-Modal mit aktuellem Wert-Label.
Bei jedem Oeffnen wird der Speed auf 1.0 zurueckgesetzt (bewusst kein
persist — nur zum Experimentieren waehrend das Modal offen ist).

- Range 0.1-5.0, gleiche wie in App-Settings
- Wird beim Play an f5tts-bridge als speed-Param mitgegeben
- Server clampt auf 0.1-5.0, Fallback 1.0

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

diagnostic/server.js

@@ -1469,7 +1469,7 @@ wss.on("connection", (ws) => {
       } else if (msg.action === "test_tts") {
         handleTestTTS(ws, msg.text || "Test");
       } else if (msg.action === "preview_voice") {
-        handleVoicePreview(ws, msg.voice || "", msg.text || "Hallo.");
+        handleVoicePreview(ws, msg.voice || "", msg.text || "Hallo.", msg.speed);
       } else if (msg.action === "check_tts") {
         handleCheckTTS(ws);
       } else if (msg.action === "check_desktop") {
@@ -1704,8 +1704,11 @@ function _handlePreviewChunk(payload) {
   }
 }
 
-async function handleVoicePreview(clientWs, voice, text) {
+async function handleVoicePreview(clientWs, voice, text, speed) {
   try {
+    // Speed clampen — Browser-Slider ist 0.1-5.0
+    let spd = parseFloat(speed);
+    if (!isFinite(spd) || spd < 0.1 || spd > 5.0) spd = 1.0;
     const requestId = crypto.randomUUID();
     _previewPending.set(requestId, { clientWs, chunks: [], sampleRate: 0, channels: 0 });
     // Timeout safety net
@@ -1720,10 +1723,10 @@ async function handleVoicePreview(clientWs, voice, text) {
         }
       }
     }, 60000);
-    log("info", "server", `Voice-Preview: voice="${voice}" text="${text.slice(0, 60)}"`);
+    log("info", "server", `Voice-Preview: voice="${voice}" speed=${spd.toFixed(1)}x text="${text.slice(0, 60)}"`);
     sendToRVS_raw({
       type: "xtts_request",
-      payload: { text, language: "de", requestId, voice, speed: 1.0 },
+      payload: { text, language: "de", requestId, voice, speed: spd },
       timestamp: Date.now(),
     });
   } catch (err) {