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/index.html

@@ -145,6 +145,15 @@
       </div>
       <textarea id="voice-preview-text" rows="4"
         style="background:#0D0D1A;border:1px solid #2A2A3E;border-radius:6px;padding:10px;color:#fff;font-size:13px;resize:vertical;"></textarea>
+
+      <div style="display:flex;align-items:center;gap:10px;font-size:12px;color:#8888AA;">
+        <span style="min-width:120px;">Geschwindigkeit:</span>
+        <button onclick="adjustPreviewSpeed(-0.1)" class="btn secondary" style="padding:4px 10px;font-size:12px;">−0.1</button>
+        <span id="voice-preview-speed-value" style="min-width:52px;text-align:center;color:#fff;font-weight:600;">1.0 x</span>
+        <button onclick="adjustPreviewSpeed(0.1)" class="btn secondary" style="padding:4px 10px;font-size:12px;">+0.1</button>
+        <span style="color:#555570;font-size:11px;">(nur fuer dieses Modal, wird nicht gespeichert)</span>
+      </div>
+
       <div style="display:flex;gap:8px;align-items:center;">
         <button id="voice-preview-play" onclick="playVoicePreview()" class="btn primary" style="padding:8px 16px;">
           ▶ Abspielen
@@ -1630,10 +1639,29 @@
 
     // ── Voice Preview Modal ─────────────────────────
     const VOICE_PREVIEW_DEFAULT = 'Hallo, ich bin ARIA. Das hier ist ein kleiner Test damit du meine Stimme beurteilen kannst.';
+    const PREVIEW_SPEED_DEFAULT = 1.0;
+    const PREVIEW_SPEED_MIN = 0.1;
+    const PREVIEW_SPEED_MAX = 5.0;
     let currentPreviewVoice = '';
+    let currentPreviewSpeed = PREVIEW_SPEED_DEFAULT;
+
+    function _refreshPreviewSpeedLabel() {
+      const el = document.getElementById('voice-preview-speed-value');
+      if (el) el.textContent = currentPreviewSpeed.toFixed(1) + ' x';
+    }
+
+    function adjustPreviewSpeed(delta) {
+      const next = Math.round((currentPreviewSpeed + delta) * 10) / 10;
+      if (next < PREVIEW_SPEED_MIN || next > PREVIEW_SPEED_MAX) return;
+      currentPreviewSpeed = next;
+      _refreshPreviewSpeedLabel();
+    }
 
     function openVoicePreview(name) {
       currentPreviewVoice = name;
+      // Speed bei jedem Oeffnen zuruecksetzen — bewusst kein persist
+      currentPreviewSpeed = PREVIEW_SPEED_DEFAULT;
+      _refreshPreviewSpeedLabel();
       document.getElementById('voice-preview-name').textContent = name;
       // Text bei jedem Oeffnen zuruecksetzen
       document.getElementById('voice-preview-text').value = VOICE_PREVIEW_DEFAULT;
@@ -1658,7 +1686,12 @@
       }
       document.getElementById('voice-preview-status').textContent = '⏳ Rendere...';
       document.getElementById('voice-preview-play').disabled = true;
-      send({ action: 'preview_voice', voice: currentPreviewVoice, text });
+      send({
+        action: 'preview_voice',
+        voice: currentPreviewVoice,
+        text,
+        speed: currentPreviewSpeed,
+      });
     }
 
     function deleteXttsVoice(name) {