Add confirmed local FFmpeg audio preparation workflow

[LittleLaXerath]

中文

用户可见变化

• 新增独立“音频准备”页面，不改变现有聊天入口与 SynthV 实时音符插入流程。
• 支持选择或拖入单个本地媒体文件，先显示时长、容器/编码、采样率和声道。
• 支持生成新的 PCM WAV，可选择采样率、单/立体声、s16/s24/f32，以及可选裁剪范围。
• 支持只读 EBU R128 响度测量，并在用户确认后生成标准化 WAV；默认值明确标记为通用试听预设，而非 SynthV 标准。
• 支持输入/输出试听、打开文件位置、复制路径和另存为。

确认、安全与组件维护

• 所有写入操作先展示输入、参数和输出位置，确认后才开始；源文件不会被覆盖。
• 输出使用唯一文件名并限制在 ~/.SynthVcopilot/output/ffmpeg；不会自动导入 SynthV、运行 CVRS、批处理或执行任意 FFmpeg 命令。
• 将组件占位页改为真实 FFmpeg 状态与维护界面，安装、更新和卸载均需确认；系统或显式配置的 FFmpeg 不会被卸载，也不修改系统 PATH。
• 增加全局任务条、跨页面单任务互斥、进度、取消、页面缓存和窗口关闭清理。

Runtime 与架构

• 新增类型化 DTO、六项 C ABI 绑定、SafeHandle 和 FfmpegService 后台任务服务。
• 修复取消/启动竞态，确保旧取消请求不会命中新任务，窗口关闭也能取消刚登记的任务。
• 修正 x64/ARM64 到 Rust target 的映射，并扩展非 GUI ABI 冒烟测试。
• 子模块固定到 pi-agent 提交 5cdb12f；对应依赖 PR：Restrict Agent FFmpeg tools to read-only inspection pi-agent#1。
• Agent 仅保留只读探测和响度分析；准备与标准化只从 Desktop 确认流程启动。
• synthv-agent-bridge、IPC v3、sv_* 工具和 add_notes 均未修改。

验证

• 真实 C ABI：probe / prepare / loudness analysis / normalization 全部通过。
• Rust：57 项测试通过，2 项按设计忽略；Clippy -D warnings 通过。
• SynthV Bridge：240 项检查通过，工作树无改动。
• XAML XML 与事件绑定检查通过；Desktop 非 XAML C# 源编译通过。
• 本机缺少 Visual Studio C++ Build Tools、MSVC linker 与 Windows SDK；完整 WinUI XAML 和 ARM64 native 构建需由正式 Windows 构建节点补跑。

完整中英文记录见 CHANGELOG.md。

English

User-visible changes

• Add a dedicated Audio Preparation page without changing Chat or the live SynthV note-insertion workflow.
• Select or drop one local media file and inspect duration, container/codec, sample rate, and channels before processing.
• Create a new PCM WAV with explicit sample-rate, mono/stereo, s16/s24/f32, and optional trim choices.
• Measure EBU R128 loudness read-only, then create a normalized WAV only after confirmation. The defaults are clearly described as a general listening preset, not a SynthV standard.
• Preview input/output audio, open the file location, copy the path, or use Save As.

Confirmation, safety, and maintenance

• Show input, parameters, and destination before every write-capable action; never overwrite the source.
• Generate unique output names under ~/.SynthVcopilot/output/ffmpeg; do not auto-import into SynthV, run CVRS, batch files, or expose arbitrary FFmpeg commands.
• Replace the component placeholder with real FFmpeg status and confirmed maintenance actions. System or explicitly configured FFmpeg remains read-only, and global PATH is never modified.
• Add a global cross-page task bar, process-wide mutual exclusion, progress, cancellation, navigation caching, and shutdown cleanup.

Runtime and architecture

• Add typed DTOs, six C ABI bindings, SafeHandle ownership, and a background FfmpegService.
• Close start/cancel races so stale cancellation cannot terminate a newer job and shutdown cancels newly registered work.
• Correct x64/ARM64 Rust target mapping and expand the non-GUI ABI smoke suite.
• Pin the submodule to pi-agent commit 5cdb12f; dependency PR: Restrict Agent FFmpeg tools to read-only inspection pi-agent#1.
• Keep only read-only probe and loudness analysis in the Agent; preparation and normalization start only from the confirmed Desktop path.
• Leave synthv-agent-bridge, IPC v3, the sv_* tools, and add_notes unchanged.

Validation

• Real C ABI passed probe, prepare, loudness analysis, and normalization.
• Rust passed 57 tests with 2 intentionally ignored; Clippy passed with -D warnings.
• SynthV Bridge passed 240 checks and remained unchanged.
• XAML XML/event binding checks and non-XAML Desktop C# source compilation passed.
• This machine lacks Visual Studio C++ Build Tools, the MSVC linker, and the Windows SDK; complete WinUI XAML and ARM64 native builds remain for a fully provisioned Windows build node.

See CHANGELOG.md for the complete bilingual release notes.

[LittleLaXerath]

Superseded by the native Tauri implementation in #2 and #3.

The original branch is intentionally preserved as a UX and test reference, but it is based on the removed WinUI/P/Invoke architecture and cannot be safely rebased onto the current Rust/Tauri mainline. The replacement keeps the confirmed-write, PCM preparation, EBU R128, progress/cancellation, preview, safe Save As, and path-safety advantages while staying close to the current codebase.

已由原生 Tauri 实现 #2 与 #3 取代。

旧分支会保留，继续作为交互与测试参考；但它基于已经移除的 WinUI/P/Invoke 架构，不能安全 rebase 到当前 Rust/Tauri 主线。新实现保留了写入确认、PCM 准备、EBU R128、进度/取消、试听、安全另存为和路径安全等优势，同时贴合当前代码库。