feat: 新增 MinIO 对象存储与算力节点缓存预下载

- 后端新增 storage 模块（minio_store），支持 MinIO 预签名 URL 上传与对象管理
- config 新增 MinIO 及存储等待相关配置项
- 算力节点新增 /compute/cache/prepare 缓存预下载接口（带校验和原子落盘）
- 算力节点健康接口增加存储可用性探针
- SQL 迁移补充资源存储相关表结构
- Docker 新增 minio 服务与后端 minio 配置
- 补充 minio-compute-cache-plan 设计文档

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/modules/compute_gateway/client.py

@@ -192,6 +192,27 @@ class ComputeNodeClient:
             response.raise_for_status()
             return _unwrap_dict(response.json())
 
+    async def prepare_cache(self, payload: dict[str, Any]) -> dict[str, Any]:
+        async with httpx.AsyncClient(timeout=httpx.Timeout(900, connect=30), headers=self.headers()) as client:
+            response = await client.post(
+                _join_url(self.api_base_url, f"{self.route_prefix}/compute/cache/prepare"),
+                json=payload,
+            )
+            response.raise_for_status()
+            return _unwrap_dict(response.json())
+
+    async def cache_status(self, resource_id: str, version_id: str | None = None) -> dict[str, Any]:
+        params = {"resource_id": resource_id}
+        if version_id:
+            params["version_id"] = version_id
+        async with httpx.AsyncClient(timeout=self.timeout, headers=self.headers()) as client:
+            response = await client.get(
+                _join_url(self.api_base_url, f"{self.route_prefix}/compute/cache/status"),
+                params=params,
+            )
+            response.raise_for_status()
+            return _unwrap_dict(response.json())
+
     async def _request(
         self,
         method: str,