feat(email): 实现邮件模板系统并添加邮件发送功能

- 新增 EmailTemplateUtil 工具类，用于管理邮件模板和发送逻辑
- 在 MainController 中集成 EmailTemplateUtil，用于发送注册成功邮件
- 添加密码重置和通用通知邮件模板
- 实现邮件发送的降级机制，HTML邮件发送失败时自动发送文本邮件
- 添加邮件模板配置和发送设置配置
- 提供异步发送和模板缓存优化建议

src/main/resources/email-templates.yml

@@ -0,0 +1,75 @@
+# 邮件模板配置文件
+# 用于管理邮件模板的基本信息和品牌设置
+
+email:
+  templates:
+    # 品牌信息
+    brand:
+      name: "WebSoft"
+      company: "南宁网宿信息科技有限公司"
+      description: "企业级数字化解决方案"
+      website: "https://www.gxwebsoft.com"
+      support_email: "170083662@qq.com"
+      logo_url: "https://www.gxwebsoft.com/logo.png"
+      
+    # 链接配置
+    links:
+      login: "https://www.gxwebsoft.com/login"
+      help: "https://www.gxwebsoft.com/help"
+      contact: "https://www.gxwebsoft.com/contact"
+      security: "https://www.gxwebsoft.com/security"
+      
+    # 模板列表
+    templates:
+      register-success:
+        name: "注册成功邮件"
+        description: "用户注册成功后发送的欢迎邮件"
+        file: "register-success.html"
+        subject: "恭喜！您的WebSoft账号已注册成功"
+        
+      password-reset:
+        name: "密码重置邮件"
+        description: "用户密码重置后发送的通知邮件"
+        file: "password-reset.html"
+        subject: "WebSoft密码重置通知"
+        
+      notification:
+        name: "通用通知邮件"
+        description: "系统通知、公告等通用邮件模板"
+        file: "notification.html"
+        subject: "WebSoft系统通知"
+        
+      security-alert:
+        name: "安全提醒邮件"
+        description: "账户安全相关的提醒邮件"
+        file: "notification.html"
+        subject: "WebSoft账户安全提醒"
+        
+      maintenance:
+        name: "系统维护通知"
+        description: "系统维护时发送的通知邮件"
+        file: "notification.html"
+        subject: "WebSoft系统维护通知"
+        
+      order-status:
+        name: "订单状态更新"
+        description: "订单状态变更时发送的通知邮件"
+        file: "notification.html"
+        subject: "WebSoft订单状态更新"
+        
+    # 邮件样式配置
+    styles:
+      primary_color: "#667eea"
+      secondary_color: "#764ba2"
+      success_color: "#4CAF50"
+      warning_color: "#ffa502"
+      danger_color: "#ff6b6b"
+      info_color: "#4facfe"
+      
+    # 邮件发送配置
+    settings:
+      retry_times: 3
+      timeout: 30000
+      fallback_to_text: true
+      track_opens: true
+      track_clicks: true