feat(voice): implementa voz y TTS en chats POS y dashboard

- Agrega TTS (speechSynthesis) a chat.js del POS para leer respuestas IA
- Copia lógica de voz completa (STT + TTS) a dashboard/chat-public.js
- Extiende estilos TTS en chat.css y chat-public.css
- Agrega chat widget a 13 templates POS que no lo tenían
- Corrige duplicado de chat.css en diagrams.html
- Minifica assets actualizados
- 73/73 tests pasan

pos/static/js/chat.js

@@ -9,8 +9,11 @@
   let isSending = false;
   let isListening = false;
   let recognition = null;
+  let ttsEnabled = true;
+  let ttsUtterance = null;
   const history = [];  // conversation history for AI context
   const hasSpeechAPI = ('webkitSpeechRecognition' in window || 'SpeechRecognition' in window);
+  const hasTTS = ('speechSynthesis' in window);
 
   // ─── Build DOM ───
   function init() {
@@ -71,6 +74,16 @@
       document.getElementById('chatMic').addEventListener('click', toggleVoice);
     }
 
+    // TTS toggle
+    if (hasTTS) {
+      document.getElementById('chatTtsToggle').addEventListener('click', toggleTTS);
+    }
+
+    // Stop TTS when closing
+    document.getElementById('chatClose').addEventListener('click', function () {
+      if (hasTTS) stopSpeaking();
+    });
+
     // Auto-resize textarea
     document.getElementById('chatInput').addEventListener('input', function () {
       this.style.height = 'auto';
@@ -170,6 +183,34 @@
     }, 2000);
   }
 
+  // ─── TTS (Text-to-Speech) ───
+  function toggleTTS() {
+    ttsEnabled = !ttsEnabled;
+    const btn = document.getElementById('chatTtsToggle');
+    if (btn) {
+      btn.classList.toggle('off', !ttsEnabled);
+      btn.setAttribute('title', ttsEnabled ? 'Desactivar lectura de respuestas' : 'Activar lectura de respuestas');
+    }
+    if (!ttsEnabled) stopSpeaking();
+  }
+
+  function speak(text) {
+    if (!hasTTS || !ttsEnabled || !text) return;
+    stopSpeaking();
+    ttsUtterance = new SpeechSynthesisUtterance(text);
+    ttsUtterance.lang = 'es-MX';
+    ttsUtterance.rate = 1.1;
+    ttsUtterance.pitch = 1;
+    window.speechSynthesis.speak(ttsUtterance);
+  }
+
+  function stopSpeaking() {
+    if (hasTTS && window.speechSynthesis.speaking) {
+      window.speechSynthesis.cancel();
+    }
+    ttsUtterance = null;
+  }
+
   // ─── Image Upload (Part identification placeholder) ───
   function handleImageUpload(e) {
     const file = e.target.files && e.target.files[0];
@@ -314,6 +355,7 @@
       const aiMsg = data.response || 'Sin respuesta.';
       addBubble(aiMsg, 'ai');
       history.push({ role: 'assistant', content: aiMsg });
+      speak(aiMsg);
 
       // Vehicle info
       if (data.vehicle && data.vehicle.brand_id) {