feat: 训练任务支持从最新 checkpoint 继续训练

- 后端: 新增 resume/checkpoints 端点，compute 客户端与适配器支持续训
- 计算节点: llama_factory 适配器断点续训支持及测试
- 前端: fine-tune API 封装与列表页续训/断点展示

backend/app/modules/compute_gateway/client.py

@@ -158,7 +158,12 @@ class ComputeNodeClient:
             return _unwrap_dict(response.json())
 
     async def stop_job(self, job_id: str) -> dict[str, Any]:
-        async with httpx.AsyncClient(timeout=self.timeout, headers=self.headers()) as client:
+        # Compute API waits for the child process to exit (up to 10 seconds)
+        # before returning.  The normal polling timeout is intentionally short,
+        # but is too aggressive for a stop request and used to surface as a
+        # platform 500 even when the node eventually stopped the job.
+        stop_timeout = max(float(self.timeout), 30.0)
+        async with httpx.AsyncClient(timeout=stop_timeout, headers=self.headers()) as client:
             response = await client.post(_join_url(self.api_base_url, f"{self.route_prefix}/compute/jobs/{job_id}/stop"))
             response.raise_for_status()
             return _unwrap_dict(response.json())