refactor(api): 优化 JSON 返回逻辑

- 将 exit(json_encode($data)) 替换为 returnJson($data) 函数
- 在 switch 语句中添加 break 语句，避免代码执行顺序错误
- 统一 JSON 返回格式，提高代码可维护性

api.php

@@ -973,7 +973,8 @@ switch ($act) {
         $data = $result->fetch_array();
         $result->free_result();
         $stmt2->close();
-        exit(json_encode($data));
+        returnJson($data);
+        break;
     case 'link':
         $stmt = $mySQLi->prepare('select player_id from player_connect_threeparty where type=`linuxdo` and connect_id=?');
         $stmt->bind_param('s', input('connect_id'));
@@ -988,10 +989,11 @@ switch ($act) {
             $getPlayer->execute();
             $res = $getPlayer->get_result();
             $account = $res->fetch_array();
-            exit(json_encode(['code' => 0, 'data' => $res]));
+            returnJson(['code' => 0, 'data' => $res]);
         } else {
-            exit(json_encode(['code' => '1']));
+            returnJson(['code' => '1']);
         }
+        break;
     default:
         echo 'success';
 }