fix(desktop): repair local setup and native macOS chrome

[Luhaozhu]

Summary / 概述

Synchronize the upstream desktop fixes into the public CE tree.

• Start local-service installation in place instead of switching configuration and restarting before installation begins.
• Keep setup progress visible, handle request failures, avoid duplicate polling timers, and switch to the local service only after its health check succeeds.
• Use native macOS traffic lights and the system application menu, with a translucent Mac toolbar containing icon-only New Chat and Service Settings actions.
• Preserve the existing compact custom window chrome on Windows and Linux.
• Add desktop PR checks on macOS and Windows so platform-specific compilation and the public CE payload path are validated before release.

Validation completed before opening this PR:

• Windows CE payload preparation succeeded from the tracked public repository tree.
• Windows Rust tests: 13 passed.
• Windows Tauri release executable build succeeded.
• Linux Rust tests: 12 passed.
• Desktop helper tests: 8 passed.
• Frontend production build and CE derivation brand gates passed.

The runtime files in this PR were derived from the upstream FULL repository; this is an official upstream synchronization rather than a direct downstream source edit.

Related issue / 关联 Issue

None.

Type of change / 变更类型

• 📖 Documentation (document/**, README*.md)
• 🧩 Example / sample (examples/**)
• 🔧 Repo meta (CI, templates, .github/**)
• Other (please describe / 请说明): Upstream-derived desktop runtime fix

Checklist / 检查项

• My change only touches non-generated paths (docs / examples / repo meta). 仅改动非生成路径。
• Links and code snippets were verified. 链接与代码片段已验证。
• For bilingual docs, I updated both document/en/** and document/zh-CN/** where applicable. 双语文档已同步更新（如适用）。
• I read CONTRIBUTING.md. 我已阅读贡献指南。