Fix desktop task header hit testing

[OldKrab]

Summary

• let integrated title-bar overlays pass pointer input to the real Task header
• preserve sidebar drag regions and native caption controls
• cover title hit-testing and the permission policy menu in the Desktop smoke test

Verification

• npx playwright test tests/smoke/desktop-new-task.spec.mjs
• npm run test --workspace openaide-frontend -- DesktopTitleBar.test.tsx TaskHeader.test.tsx
• npm run check --workspace openaide-frontend