Support update notifications on Windows

YU
7h ago
+40-30

Extend the update-check platform condition to include Windows builds. This allows Windows users to receive update notifications through the existing update-check mechanism, while keeping the feature opt-in.
Closes #547

Summary by cubic

Extends update-check notifications to Windows builds so Windows users receive update notices, where previously the check ran only on macOS. The feature stays opt-in and only runs on CI builds with a release commit.

  • update_check_commit now takes a supported_platform flag instead of a macos flag, keeping the platform rule testable on Linux runners; the test suite covers the setting, platform, and CI-commit requirements.
  • src/main.rs enables the check on macOS and Windows.
  • The Windows release build now receives GITHUB_SHA in CI so it has a release commit to compare against.
  • docs/install.md updated to reflect that the update check runs on macOS and Windows, not on Linux or in source builds.

Closes #547.