feat: 实现联系表单提交与邮件通知功能

添加联系表单提交接口和邮件通知功能，支持从环境变量读取 SMTP 配置
重构 SEO 配置到 site.json，新增 robots.txt 和 sitemap.xml 生成
更新公司电话并添加 PM2 生产运行配置

data/site.json

@@ -7,10 +7,46 @@
     "founded": "2018",
     "employees": "500+",
     "address": "上海市浦东新区张江高科技园区博云路2号",
-    "phone": "400-888-6688",
+    "phone": "400-888-8888",
     "email": "bd@zhidiansoft.com",
     "icp": "沪ICP备XXXXXXXX号"
   },
+  "seo": {
+    "siteUrl": "https://www.zhidiansoft.com",
+    "siteName": "智店软件",
+    "defaultTitle": "连锁门店收银、分账、监管系统 | 智店软件",
+    "titleTemplate": "%s | 智店软件",
+    "description": "面向连锁餐饮、零售与加盟品牌，提供门店收银、自动分账、总部监管一体化系统定制与升级服务。兼容现有设备与流程，支持不停业切换。",
+    "keywords": [
+      "连锁门店系统",
+      "收银系统",
+      "自动分账系统",
+      "总部监管系统",
+      "加盟门店结算",
+      "门店数字化",
+      "智店软件"
+    ],
+    "canonicalPath": "/",
+    "locale": "zh_CN",
+    "robots": {
+      "index": true,
+      "follow": true
+    },
+    "openGraph": {
+      "type": "website",
+      "image": "/images/hero-bg.jpg"
+    },
+    "twitter": {
+      "card": "summary_large_image"
+    },
+    "verification": {
+      "google": "",
+      "yandex": "",
+      "other": {
+        "baidu-site-verification": ""
+      }
+    }
+  },
   "nav": {
     "links": [
       { "label": "首页", "href": "#home" },