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>

docker/app/docker-compose.yml

@@ -62,6 +62,14 @@ services:
       COMPUTE_POLL_INTERVAL_SECONDS: ${COMPUTE_POLL_INTERVAL_SECONDS:-3}
       COMPUTE_POLL_BATCH_SIZE: ${COMPUTE_POLL_BATCH_SIZE:-100}
       COMPUTE_REQUEST_TIMEOUT_SECONDS: ${COMPUTE_REQUEST_TIMEOUT_SECONDS:-5}
+      MINIO_ENABLED: ${MINIO_ENABLED:-false}
+      MINIO_ENDPOINT: ${MINIO_ENDPOINT:-http://minio:9000}
+      MINIO_ACCESS_KEY: ${MINIO_ACCESS_KEY:-minioadmin}
+      MINIO_SECRET_KEY: ${MINIO_SECRET_KEY:-minioadmin}
+      MINIO_BUCKET: ${MINIO_BUCKET:-yg-ft-resources}
+      MINIO_SECURE: ${MINIO_SECURE:-false}
+      STORAGE_WAIT_SECONDS: ${STORAGE_WAIT_SECONDS:-300}
+      STORAGE_CHECK_INTERVAL_SECONDS: ${STORAGE_CHECK_INTERVAL_SECONDS:-10}
       PYTHONPATH: /app
     volumes:
       - ../../backend:/app:ro