refactor(email): 简化邮件通知设置逻辑

移除adminEnabled和userEnabled配置，仅保留globalEnabled控制邮件通知
更新相关API、数据库操作及邮件发送逻辑以适配简化后的配置

cwd-comments-admin/src/api/admin.ts

@@ -42,8 +42,6 @@ export type CommentSettingsResponse = {
 
 export type EmailNotifySettingsResponse = {
 	globalEnabled: boolean;
-	adminEnabled: boolean;
-	userEnabled: boolean;
 };
 
 export async function loginAdmin(name: string, password: string): Promise<string> {
@@ -83,8 +81,6 @@ export function fetchEmailNotifySettings(): Promise<EmailNotifySettingsResponse>
 
 export function saveEmailNotifySettings(data: {
 	globalEnabled?: boolean;
-	adminEnabled?: boolean;
-	userEnabled?: boolean;
 }): Promise<{ message: string }> {
 	return put<{ message: string }>('/admin/settings/email-notify', data);
 }

cwd-comments-admin/src/views/LayoutView.vue

@@ -8,7 +8,7 @@
           href="https://cwd-comments-docs.zishu.me"
           target="_blank"
         >
-          文档
+          使用文档
         </a>
         <a
           class="layout-button"