feat(learning-auth): add optional JWT learning flow with secure demo endpoint

src/main/java/com/example/demo/controller/LearnController.java

@@ -45,7 +45,9 @@ public class LearnController {
             "POST /learn/body - JSON 请求体示例",
             "GET  /learn/path/{id} - 路径变量示例",
             "GET  /learn/header - 请求头示例",
-            "GET  /learn/cookie - Cookie 示例"
+            "GET  /learn/cookie - Cookie 示例",
+            "POST /api/auth/login - 学习用 JWT 登录",
+            "GET  /api/secure/me - 受保护接口（需 Bearer Token）"
         });
         return info;
     }