refactor: v2 重构 — 模块化拆分 + AI Prompt模板化 + 前端状态管理

P0 - AI交互层:
- ai/prompt.js: 模块化 Prompt 模板
- ai/validator.js: JSON Schema 校验 + normalize
- ai/client.js: DeepSeek API 封装
- 金额计算唯一化，时间格式归一化

P1 - 后端架构:
- routes/: auth/rooms/messages/purchases 独立路由
- middleware/auth.js: 认证授权中间件
- ws/index.js: WebSocket 连接管理
- db.js: 启用 foreign_keys
- server.js: 从588行精简到40行入口

P2 - 前端架构:
- public/css/style.css: CSS 独立
- public/js/store.js: 全局状态 Store
- public/js/{chat,ws,purchases,auth}.js: 功能模块拆分
- index.html: 纯 HTML 结构, v2.6

server/routes/purchases.js

@@ -0,0 +1,48 @@
+// 采购相关路由
+const express = require('express');
+const { authMiddleware } = require('../middleware/auth');
+const db = require('../db');
+
+const router = express.Router();
+
+router.get('/rooms/:roomId/purchases', authMiddleware, (req, res) => {
+  const purchases = db.prepare('SELECT * FROM purchases WHERE room_id = ? ORDER BY created_at DESC').all(req.params.roomId);
+  res.json(purchases);
+});
+
+router.get('/purchases/:id', authMiddleware, (req, res) => {
+  const pur = db.prepare('SELECT * FROM purchases WHERE id = ?').get(req.params.id);
+  if (!pur) return res.status(404).json({ error: '未找到' });
+  const history = db.prepare('SELECT * FROM purchase_history WHERE purchase_id = ? ORDER BY id ASC').all(req.params.id);
+  const attachments = db.prepare('SELECT * FROM purchase_attachments WHERE purchase_id = ?').all(req.params.id);
+  res.json({ ...pur, history, attachments });
+});
+
+router.get('/summary', authMiddleware, (req, res) => {
+  const username = req.user.username;
+  const isAdmin = req.user.isAdmin;
+  let rooms;
+  if (isAdmin) {
+    rooms = db.prepare('SELECT id, name FROM rooms').all();
+  } else {
+    rooms = db.prepare("SELECT id, name FROM rooms WHERE white_list = '' OR (',' || white_list || ',' LIKE ?)").all(`%,${username},%`);
+  }
+  const summary = rooms.map(room => {
+    const stats = db.prepare('SELECT COUNT(*) as count, SUM(amount) as total FROM purchases WHERE room_id = ?').get(room.id);
+    return { room_id: room.id, room_name: room.name, purchase_count: stats.count || 0, total_amount: stats.total || 0 };
+  });
+  res.json(summary);
+});
+
+router.get('/rooms/:roomId/purchases/export', authMiddleware, (req, res) => {
+  const purchases = db.prepare('SELECT * FROM purchases WHERE room_id = ?').all(req.params.roomId);
+  let csv = '时间,事项,数量,单价,金额,邮费,付款方式,发票类型,状态,申请人,备注\n';
+  purchases.forEach(p => {
+    csv += `${p.created_at},"${p.item||''}",${p.quantity},${p.unit_price},${p.amount},${p.freight},"${p.payment_method||''}","${p.invoice_type||''}","${p.status}","${p.applicant}","${p.remarks||''}"\n`;
+  });
+  res.setHeader('Content-Type', 'text/csv; charset=utf-8');
+  res.setHeader('Content-Disposition', `attachment; filename="purchases-${req.params.roomId}.csv"`);
+  res.send('\uFEFF' + csv);
+});
+
+module.exports = router;