Add smart ACK provider for WeChat MP replies

Replace fixed ackText with a rule-based AckProvider that picks
response templates by message type and intent (translate, summary,
rewrite, poster, ppt, mindmap, code, search, schedule). Pure sync,
zero I/O, auto-falls back to config.ackText on any error.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/context/ChatProvider.tsx

@@ -1,5 +1,6 @@
 import { createContext, useContext, type ReactNode } from 'react';
 import { RechargeModal } from '../components/RechargeModal';
+import { SubscribeModal } from '../components/SubscribeModal';
 import { useTKMindChat } from '../hooks/useTKMindChat';
 import type { CapabilityMap, PortalUser } from '../types';
 
@@ -36,6 +37,17 @@ export function ChatProvider({
           }}
         />
       )}
+      <SubscribeModal
+        open={chat.subscribePrompt}
+        onClose={chat.dismissSubscribe}
+        onSuccess={(subscription, balanceCents) => {
+          chat.completeSubscribe(balanceCents, subscription);
+        }}
+        onRechargeNeeded={() => {
+          chat.dismissSubscribe();
+          chat.openRecharge(false);
+        }}
+      />
     </ChatContext.Provider>
   );
 }