feat: add CORS configuration for frontend development

demo_backend/src/main/java/org/example/demo_backend/config/CorsConfig.java

@@ -0,0 +1,23 @@
+package org.example.demo_backend.config;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.servlet.config.annotation.CorsRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+
+/**
+ * CORS 配置，允许前端开发阶段从 DevEco Studio 模拟器 / 浏览器跨域访问后端 API。
+ * 生产环境部署时应将 allowedOrigins 限制为具体域名。
+ */
+@Configuration
+public class CorsConfig implements WebMvcConfigurer {
+
+    @Override
+    public void addCorsMappings(CorsRegistry registry) {
+        registry.addMapping("/api/**")
+                .allowedOriginPatterns("*")
+                .allowedMethods("GET", "POST", "PUT", "DELETE", "OPTIONS")
+                .allowedHeaders("*")
+                .allowCredentials(true)
+                .maxAge(3600);
+    }
+}