feat: 本地 uv 与托管 Python 环境管理

- 新增 uv 管理：只认程序目录副本或指定路径，支持从科大镜像下载并按 sha256 校验

- uv 环境变量（UV_*）可配置，默认相对程序目录（python / uv-cache），同时注入 uv 调用与任务进程

- 新增托管虚拟环境与 Python 版本管理：用 uv 下载解释器、预创建环境、查看已装包

- 新建任务保存时自动创建 .venv，运行期只校验、不再自动装依赖；镜像只在装包时使用

- 前端改为顶部品牌栏 + 三栏工作台，uv / 镜像源 / 虚拟环境各自独立弹窗

- 发布包构建后去掉工作区继承的低完整性标签

- 修复调度集成测试并发时误取 skipped 运行的问题

backend/Cargo.toml

@@ -14,6 +14,7 @@ futures-util = { version = "0.3.34", features = ["std"] }
 reqwest = { version = "0.13.5", default-features = false, features = ["json", "rustls", "stream"] }
 serde = { version = "1.0.229", features = ["derive"] }
 serde_json = "1.0.154"
+sha2 = "0.11.1"
 sqlx = { version = "0.9.0", default-features = false, features = ["runtime-tokio", "sqlite", "sqlite-bundled", "migrate", "chrono", "derive", "macros"] }
 thiserror = "2.0.21"
 tokio = { version = "1.53.3", features = ["full"] }
@@ -27,6 +28,7 @@ utoipa = { version = "6.0.0", features = ["axum_extras", "chrono"] }
 utoipa-axum = "0.3.0"
 uuid = { version = "1.28.0", features = ["v4"] }
 windows-sys = { version = "0.61.2", features = ["Win32_Foundation", "Win32_Globalization", "Win32_Security", "Win32_Storage_FileSystem", "Win32_System_JobObjects"] }
+zip = { version = "9.4.1", default-features = false, features = ["deflate"] }
 
 [dev-dependencies]
 http-body-util = "0.1.5"