mweinbach4/30/2026, 2:47:29 PM

Add a single PlatformChromeContract module as the source of truth for
native window behavior on macOS, Windows, and Linux. Both the Electron
main-process window chrome and the renderer now read from the same
contract instead of hardcoding platform constants.

- Add electron/services/windowChrome/platformChrome.ts with per-platform
  titlebar height, drag strip, native reserves, window material, and
  sidebar/topbar placement flags.
- Refactor darwin.ts, win32.ts, linux.ts to consume the contract via
  getPlatformChrome() and getTitlebarSymbolColor().
- Update windowAppearancePaint.ts to resolve Windows background material
  through the contract.
- Add platform-chrome.test.ts covering all three platforms plus the
  fallback.

No visual changes; existing window-enhancements and
window-appearance-paint tests still pass against the same class names,
BrowserWindow options, and overlay values.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

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