feat(tts): multi-voice switcher for EN & RU, Irina default voice, punctuation pause normalization and speed calibration

app/static/js/modules/api.js

@@ -185,8 +185,12 @@ export const api = {
 
     // Listening Comprehension Trainer
     listening: {
-        async getExercise(topic = 'all', level = 'B1') {
-            const resp = await fetch(`/api/listening/exercise?topic=${encodeURIComponent(topic)}&level=${encodeURIComponent(level)}`);
+        async getExercise(topic = 'all', level = 'B1', voice = null) {
+            let url = `/api/listening/exercise?topic=${encodeURIComponent(topic)}&level=${encodeURIComponent(level)}`;
+            if (voice) {
+                url += `&voice=${encodeURIComponent(voice)}`;
+            }
+            const resp = await fetch(url);
             if (resp.ok) return await resp.json();
             throw new Error(`Failed to load listening exercise: ${resp.status}`);
         },
@@ -206,6 +210,14 @@ export const api = {
         }
     },
 
+    // Neural Speech Synthesis (TTS)
+    tts: {
+        async getStatus() {
+            const resp = await fetch('/api/tts/status');
+            return resp.ok ? await resp.json() : null;
+        }
+    },
+
     // Bookshelf & Reader
     books: {
         async getAll() {