fix(windows): reveal wallpaper behind settings

[silvermoon89]

Summary

• make the settings route use a continuous translucent main surface
• clear the nested opaque settings background so the wallpaper remains visible
• keep settings navigation and cards readable with scoped overlays

Tests

• node windows/tests/renderer-inject.test.mjs
• node windows/tests/injector-bootstrap.test.mjs
• powershell.exe -NoProfile -ExecutionPolicy Bypass -File windows/tests/run-tests.ps1
• git diff --check

[Fei-Away]

Thanks for the contribution! We just merged #216, unifying the macOS/Windows skin runtime into a single source (runtime/ + tools/selectors.json, attribute-driven rendering) — it rewrote the files this PR touches, so it's no longer compatible as submitted. Closing for now; a fresh PR against the new runtime would be very welcome if the idea still applies. Thanks again for the time you put into this!

感谢贡献！我们刚合并了 #216，把双端换肤 runtime 统一成了单一源码（runtime/ + tools/selectors.json，属性驱动渲染），这个 PR 改动的文件已经被那次重构重写，现在不再适用。先关闭，如果思路还有价值，非常欢迎基于新架构重新提一个 PR。谢谢你花的时间！