feat(邮件通知): 添加SMTP邮件发送支持并完善通知设置

- 新增nodemailer依赖实现SMTP邮件发送功能
- 扩展邮件通知设置界面，支持SMTP服务器配置
- 实现SMTP与原有邮件网关的自动切换逻辑
- 优化邮件通知相关API接口和数据库存储结构

cwd-comments-api/package.json

@@ -11,6 +11,7 @@
 	},
 	"devDependencies": {
 		"@cloudflare/vitest-pool-workers": "^0.8.19",
+		"@types/nodemailer": "^7.0.5",
 		"@types/ua-parser-js": "^0.7.39",
 		"typescript": "^5.5.2",
 		"vitest": "~3.2.0",
@@ -18,6 +19,7 @@
 	},
 	"dependencies": {
 		"hono": "^4.11.3",
+		"nodemailer": "^7.0.12",
 		"ua-parser-js": "^2.0.7"
 	}
 }