Flow 0.4.15 · Windows 10 mpv extraction fix

修复 Windows 10 上首次配置播放器时“解压失败”：Flow 之前将经过 SHA-256 校验的 mpv 7z 包交给系统 tar.exe，但部分 Win10 环境不能解压该格式。现在 Flow 内置 Rust 7z 解压，不依赖系统 tar 或外部脚本；失败时显示具体原因。可选的 setup-player.ps1 也改为调用同一安装流程。保留现有 runtime/mpv、下载文件和配置。

Fix first-run mpv setup on Windows 10. Flow previously passed a verified 7z archive to Windows tar.exe, whose 7z support is inconsistent across Win10 installations. Flow now extracts it with a built-in Rust decoder and reports specific errors. The optional setup-player.ps1 uses the same installer. Existing player runtime, downloads and settings are preserved.

Validation: the pinned 7z archive SHA-256 matched, in-process extraction produced mpv.exe, 62 application tests passed (3 optional integration tests skipped), 9 installer and 2 uninstaller tests passed. Packaged backend startup, player installer CLI, signed update manifest, checksums and portable ZIP contents verified. A Windows 10 machine was not available for GUI testing.

下载：Flow-Setup-0.4.15-x64.exe 为安装包；Flow-0.4.15-windows-x64-portable.zip 为绿色包；已有用户可完全退出 Flow 后替换 Flow.exe。 / Downloads: installer, portable ZIP, or standalone Flow.exe. Fully exit Flow before updating.