fix(desktop): add macOS 27 WebKit scroll workaround

[murongg]

Summary

• Add a macOS 27-only WebKit scrolling workaround marker based on the desktop OS version.
• Keep Markra custom scrollbars visible while the workaround is active.
• Cover platform detection, root attribute cleanup, and scrollbar styles with focused tests.

Why

• The crash log points at a macOS 27 WebKit scrolling tree failure inside WKWebView.
• The workaround is scoped to macOS 27.x so other platforms and macOS releases keep their existing behavior.

Validation

• pnpm --filter @markra/app exec vitest run src/styles.test.ts -t "visible scrollbars" passed
• pnpm --filter @markra/app exec vitest run src/lib/platform.test.ts passed
• pnpm --filter @markra/app exec vitest run src/App.test.tsx -t "WebKit scrolling workaround" passed
• pnpm --filter @markra/app build passed
• pnpm --filter @markra/desktop build passed
• pnpm --filter @markra/web build passed

Risk

• This is a targeted WKWebView workaround, not a root WebKit fix. It can be removed or narrowed when macOS/WebKit behavior stabilizes.

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Project	Deployment	Actions	Updated (UTC)
markra-web	Ready	Preview, Comment	Jun 19, 2026 3:19am