PLAN: S5 — 聊天列表页

Goal

新增 AI 聊天页面 /chat，包含左侧会话列表 + 右侧消息区域。

Current

• chat.html exists but serves WeChat talker chats (different layout)
• No /chat (without talker) route for AI chat
• S2 APIs exist: GET /api/conversations (list), POST /api/conversations (create)

Tasks

1. Add @app.route("/chat") → renders new aichat.html template
2. Create aichat.html:
   • Left sidebar (260px): "+ 新建对话" button + scrollable conversation list
   • Right area: placeholder for S6's chat interface
   • JS: fetch /api/conversations, render list, click to select, new button POSTs

Files

• app.py: add route
• templates/aichat.html: new template

Verification

• curl /chat → HTTP 200 + HTML contains sidebar elements
• Smoke test passes