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/db/sql/001_platform_runtime.sql

@@ -234,6 +234,39 @@ CREATE TABLE IF NOT EXISTS resource_sync_jobs (
     completed_at TEXT
 );
 
+CREATE TABLE IF NOT EXISTS storage_objects (
+    id TEXT PRIMARY KEY,
+    resource_type TEXT NOT NULL,
+    resource_id TEXT NOT NULL,
+    version_id TEXT NOT NULL,
+    bucket TEXT NOT NULL,
+    object_key TEXT NOT NULL,
+    file_name TEXT,
+    content_type TEXT,
+    checksum_sha256 TEXT,
+    byte_size BIGINT NOT NULL DEFAULT 0,
+    status TEXT NOT NULL DEFAULT 'pending',
+    created_by TEXT,
+    create_time TEXT NOT NULL,
+    UNIQUE (resource_type, resource_id, version_id, object_key)
+);
+
+CREATE TABLE IF NOT EXISTS storage_cache_jobs (
+    id TEXT PRIMARY KEY,
+    storage_object_id TEXT NOT NULL REFERENCES storage_objects(id) ON DELETE CASCADE,
+    node_id TEXT NOT NULL REFERENCES compute_nodes(id) ON DELETE CASCADE,
+    direction TEXT NOT NULL,
+    status TEXT NOT NULL,
+    progress INTEGER NOT NULL DEFAULT 0,
+    local_path TEXT,
+    error TEXT,
+    create_time TEXT NOT NULL,
+    completed_at TEXT
+);
+
+CREATE INDEX IF NOT EXISTS idx_storage_objects_resource ON storage_objects(resource_type, resource_id, version_id);
+CREATE INDEX IF NOT EXISTS idx_storage_cache_jobs_node_status ON storage_cache_jobs(node_id, status);
+
 CREATE TABLE IF NOT EXISTS eval_tasks (
     id TEXT PRIMARY KEY,
     name TEXT NOT NULL,
@@ -319,9 +352,14 @@ CREATE TABLE IF NOT EXISTS roles (
 CREATE TABLE IF NOT EXISTS sessions (
     id TEXT PRIMARY KEY,
     user_id TEXT NOT NULL,
-    issued_at TEXT NOT NULL,
-    expires_at TEXT NOT NULL,
-    ip TEXT
+    username TEXT,
+    login_at TEXT,
+    logout_at TEXT,
+    duration_seconds INTEGER,
+    issued_at TEXT,
+    expires_at TEXT,
+    ip TEXT,
+    create_time TEXT
 );
 
 CREATE TABLE IF NOT EXISTS acls (