mweinbach4/30/2026, 2:47:37 PM

Wire the platform chrome contract through the WebSocket-first IPC layer
so the renderer can read normalized platform info without hardcoding
process.platform checks.

- Add DESKTOP_IPC_CHANNELS.getPlatformChrome returning a
  PlatformChromeInfo snapshot.
- Expose getPlatformChrome() on the preload bridge and
  desktopCommands.ts.
- In App.tsx, write contract values onto document.documentElement as
  CSS variables (--platform-titlebar-height, etc.) and data-attrs
  (data-sidebar-titleband-mode, data-topbar-control-placement,
  data-uses-native-glass, data-disable-css-blur).
- Add src/lib/desktopPlatform.ts + useDesktopPlatform() hook for
  components to consume normalized platform info.
- Backfill getPlatformChrome() on the web adapter with a sensible
  web-mode default.

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