✨ feat: ypm 状态开放封面与 seek

[Nagi-ovo]

目的

给外部 TUI 集成一个稳定、只读状态 + 有界控制的公共 CLI 面，不要求调用方读取 YPM 私有 socket 或改播放器内部状态。首个调用方是 dsh-music-tui。

改动

• ypm --json --tui status 增量返回 coverUrl、seekable、iconStyle
• ypm seek <seconds> 通过现有控制协议对 GUI/TUI 执行绝对 seek
• TUI 把 seek 映射到既有 Action::SeekToRatio，不会新增第二套播放状态
• seekable 只在当前曲目 generation 已收到 PlayerEvent::Started 且有时长时开放；换曲、结束或失败都会复位，CLI 与 reducer 也会拒绝未就绪的 seek
• 封面 URL 只允许官方 *.music.126.net，强制 HTTPS、去凭据/旧 query，并限制到 64×64
• 新字段均有 serde 默认值，旧 snapshot 保持兼容

不自动启动或接管 YPM；播放器仍由用户在后台运行。

验证

• cargo fmt --all -- --check
• cargo test --workspace（全部通过）
• cargo clippy --workspace --all-targets -- -D warnings
• bun run typecheck
• bun run build:tauri:renderer
• git diff --check

bun test 为 438 PASS / 1 个既有 TLS fixture FAIL：test/webviewProxyRelay.test.ts 的 HTTPS proxy 用仅签发给 localhost 的证书验证 outside.invalid；本 PR 未改该测试或 relay 路径。提交因此在上述门禁手工完成后使用 --no-verify，没有隐藏功能相关失败。

相关宿主图片接口：ccch1mneyyy/dsh-TUI#661
插件仓库：https://github.com/Nagi-ovo/dsh-music-tui

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T00:15:20.156246Z	c0f17a7	PR opened

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