优化目录结构

backend/src/main/java/com/openisle/controller/AdminController.java

@@ -0,0 +1,16 @@
+package com.openisle.controller;
+
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+import java.util.Map;
+
+/**
+ * Simple admin demo endpoint.
+ */
+@RestController
+public class AdminController {
+    @GetMapping("/api/admin/hello")
+    public Map<String, String> adminHello() {
+        return Map.of("message", "Hello, Admin User");
+    }
+}