feat: 添加注册开关功能，优化系统配置与注册接口

server/middleware/registration-guard.ts

@@ -0,0 +1,22 @@
+// server/middleware/registration-guard.ts - 注册开关守卫
+//
+// 拦截 POST /api/auth/sign-up/email，若系统配置关闭了注册，立即返回 403。
+// 此中间件优先于 Better Auth catch-all handler 执行，无需改动 auth.ts。
+
+import { getRequestURL, setResponseStatus } from "h3";
+
+import { apiErr } from "~~/server/utils/response";
+import { getSysConfig } from "~~/server/utils/sysConfig";
+
+export default defineEventHandler(async (event) => {
+  const { pathname } = getRequestURL(event);
+
+  // 只拦截注册接口
+  if (pathname !== "/api/auth/sign-up/email" || event.method !== "POST") return;
+
+  const cfg = await getSysConfig();
+  if (!cfg.allowRegistration) {
+    setResponseStatus(event, 403);
+    return apiErr(403, "当前未开启注册");
+  }
+});