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

dashboard/chat-public.min.css

@@ -1,5 +1,5 @@
 /* ==========================================================================
-   NEXUS — Public Catalog Chat Widget
+   NEXUS — Public Catalog Chat Widget (Voice + TTS enabled)
    Reuses design tokens from tokens.css
    ========================================================================== */
 
@@ -228,6 +228,99 @@
 .chat-send-btn:hover { background: var(--color-primary-hover, #e5952f); }
 .chat-send-btn:disabled { opacity: 0.5; cursor: not-allowed; }
 
+/* ─── Header Actions (TTS toggle + close) ─── */
+.chat-header-actions {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.chat-tts-toggle {
+  background: none;
+  border: none;
+  color: #fff;
+  font-size: 1rem;
+  cursor: pointer;
+  padding: 4px;
+  line-height: 1;
+  opacity: 0.9;
+  transition: opacity 0.15s ease;
+}
+
+.chat-tts-toggle:hover { opacity: 1; }
+.chat-tts-toggle.off { opacity: 0.4; }
+
+/* ─── Mic Button (Voice Input) ─── */
+.chat-mic-btn {
+  width: 38px;
+  height: 38px;
+  border-radius: 8px;
+  border: 1px solid var(--color-border, #333);
+  background: var(--color-bg-base, #111);
+  color: var(--color-text-secondary, #aaa);
+  font-size: 1.1rem;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-shrink: 0;
+  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease;
+}
+
+.chat-mic-btn:hover {
+  border-color: var(--color-accent, #F5A623);
+  color: var(--color-accent, #F5A623);
+}
+
+.chat-mic-btn.listening {
+  background: #f85149;
+  border-color: #f85149;
+  color: #fff;
+  animation: micPulse 1.4s infinite;
+}
+
+@keyframes micPulse {
+  0%, 100% { box-shadow: 0 0 0 0 rgba(248, 81, 73, 0.4); }
+  50% { box-shadow: 0 0 0 10px rgba(248, 81, 73, 0); }
+}
+
+/* ─── TTS Button ─── */
+.chat-tts-btn {
+  background: none;
+  border: none;
+  color: #8b949e;
+  font-size: 0.85rem;
+  cursor: pointer;
+  padding: 2px 4px;
+  margin-left: 6px;
+  border-radius: 4px;
+  transition: color 0.2s, background 0.2s;
+}
+.chat-tts-btn:hover { color: #58a6ff; background: rgba(88,166,255,0.1); }
+.chat-tts-btn.tts-active { color: #58a6ff; }
+
+/* ─── Voice Toast ─── */
+.chat-voice-toast {
+  position: fixed;
+  bottom: 160px;
+  left: 50%;
+  transform: translateX(-50%) translateY(10px);
+  background: rgba(0, 0, 0, 0.8);
+  color: #fff;
+  padding: 8px 18px;
+  border-radius: 8px;
+  font-size: 0.85rem;
+  z-index: 9999;
+  opacity: 0;
+  transition: opacity 0.3s, transform 0.3s;
+  pointer-events: none;
+}
+
+.chat-voice-toast.visible {
+  opacity: 1;
+  transform: translateX(-50%) translateY(0);
+}
+
 @media (max-width: 480px) {
   .chat-panel {
     width: calc(100vw - 16px);