refactor: 跨 Token 重试次数改为读取 retry.max_retry 配置

将 ChatService 中跨 Token 重试的硬编码 max_token_retries=3 改为
从 retry.max_retry 配置项读取，与内层重试机制保持一致。

app/services/grok/services/chat.py

@@ -402,7 +402,7 @@ class ChatService:
 
         # 跨 Token 重试循环
         tried_tokens = set()
-        max_token_retries = 3
+        max_token_retries = int(get_config("retry.max_retry"))
         last_error = None
 
         for attempt in range(max_token_retries):