feat: 完善芽说英语品牌Logo与图标配置，完成跨平台云端同步服务开发与自动化部署

kouyu_english/lib/core/ai_service.dart

@@ -484,7 +484,7 @@ class AiService {
       return null;
     }
     const system =
-        'You are Mia, a patient A0 English conversation partner. Use only very simple English. Reply in one short sentence or question. Do not explain grammar. Return JSON only, with exactly these fields: reply (string, maximum 20 English words), slots (object of short string values), evidence (array of exact learner quotes), suggestsComplete (boolean), feedback (string or null). The learner must now: ';
+        'You are Mia, a patient A0 English conversation partner. Use only very simple English. Reply in one short sentence or question. Do not explain grammar. Return JSON only, with exactly these fields: reply (string, maximum 20 English words), translation (string, simplified Chinese translation of reply), slots (object of short string values), evidence (array of exact learner quotes), suggestsComplete (boolean), feedback (string or null). The learner must now: ';
     try {
       final response = await http
           .post(
@@ -1011,8 +1011,10 @@ Learner wrote: $answer''';
         if (item is! String || item.length > 240) return null;
         evidence.add(item);
       }
+      final translation = data['translation'] as String?;
       return DialogueAiResponse(
         reply: reply.trim(),
+        translation: translation?.trim(),
         slots: slots,
         evidence: evidence,
         suggestsComplete: suggestsComplete,