新增清潔費欄位 {{清潔費}}，並記憶每份範本上次使用的值

- 表單新增「清潔費」欄位，預設 1200
- 後端 PDF 產生成功後自動將 monthlyRent / paymentDay / deposit / cleaningFee
  寫入 templates/defaults.json，key 為範本檔名
- 切換範本時呼叫 /api/templates/:name/defaults 自動帶入上次的值
- 表單版面調整為 2x2：每月租金/繳款日期、保證金/清潔費 各一行
- 4 份逢甲範本加入 {{清潔費}} 佔位符

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

server.js

@@ -7,6 +7,8 @@ const {
   getTemplatePreviewPdf,
   saveTemplate,
   deleteTemplate,
+  getTemplateDefaults,
+  saveTemplateDefaults,
 } = require('./src/contractService');
 
 const app = express();
@@ -61,6 +63,14 @@ app.get('/api/templates', async (_req, res, next) => {
   }
 });
 
+app.get('/api/templates/:name/defaults', async (req, res, next) => {
+  try {
+    res.json(await getTemplateDefaults(req.params.name));
+  } catch (error) {
+    next(error);
+  }
+});
+
 app.get('/api/templates/:name/preview', async (req, res) => {
   try {
     const pdfBuffer = await getTemplatePreviewPdf(req.params.name, req.query);
@@ -82,10 +92,18 @@ app.post('/api/contracts/pdf', async (req, res) => {
       monthlyRent: req.body.monthlyRent,
       paymentDay: req.body.paymentDay,
       deposit: req.body.deposit,
+      cleaningFee: req.body.cleaningFee,
       leaseStart: req.body.leaseStart,
       leaseEnd: req.body.leaseEnd,
     });
 
+    await saveTemplateDefaults(req.body.template, {
+      monthlyRent: req.body.monthlyRent,
+      paymentDay: req.body.paymentDay,
+      deposit: req.body.deposit,
+      cleaningFee: req.body.cleaningFee,
+    }).catch(() => {});
+
     res.setHeader('Content-Type', 'application/pdf');
     res.setHeader(
       'Content-Disposition',