feat(gateway): 迁移 manage-gateway 模块主代码（任务 T3.1）

- 删除 novalon manage-gateway 现有 Java 源代码
- 从 gym-manage 复制 37 个 Java 文件并替换包名 cn.novalon.gym.manage → cn.novalon.manage
- 编译验证通过

novalon-manage-api/manage-gateway/src/main/java/cn/novalon/manage/gateway/service/impl/JwtKeyServiceImpl.java

@@ -198,6 +198,8 @@ public class JwtKeyServiceImpl implements JwtKeyService {
         try {
             String initialKey;
             
+            logger.info("Configured JWT secret: {}", configuredSecret != null ? "present (length: " + configuredSecret.length() + ")" : "null");
+            
             if (configuredSecret != null && !configuredSecret.isEmpty()) {
                 if (configuredSecret.startsWith("enc:")) {
                     initialKey = decryptKey(configuredSecret.substring(4));
@@ -216,6 +218,8 @@ public class JwtKeyServiceImpl implements JwtKeyService {
                 logger.info("Generated new secure JWT key");
             }
             
+            logger.info("JWT key length: {}", initialKey.length());
+            
             SecretKey signingKey = new SecretKeySpec(
                     initialKey.getBytes(StandardCharsets.UTF_8),
                     KEY_ALGORITHM