[adokce]

macOS windows have no draggable area while the standalone loading screen is visible because the regular toolbar has not mounted yet. This can leave the window stuck in place for the entire “Building walkthrough…” step.

Add a desktop-only, 40-pixel drag region across the top of the window during bootstrap, repository/walkthrough/plan loading, and standalone startup errors. It is attached to the root so the loading message's transforms and pulse animation do not move it, and disappears when the normal app toolbar renders.

Validation:

• Six regression cases cover startup/loading/error screens and the transition to the normal toolbar.
• Verified in Electron that the region has the expected native drag behavior and disappears after loading; also dragged a macOS test window while “Building walkthrough…” remained visible.
• vp check --fix passed.
• vp test passed: 1,295 tests passed, 4 skipped.
• vpr build passed.

This PR was written and tested with OpenAI Codex, including diagnosis, implementation, tests, and the PR description.

banana banana banana

[cpojer]

Thanks.