GPUI: Four titlebar buttons do not respond on Windows

[maddada]

Environment

• GPUI app
• Windows

Problem

Clicking any of the four buttons at the top-right of the GPUI app titlebar does not perform the corresponding action.

Expected behavior

Each titlebar button should respond to clicks and perform its intended action.

[maddada]

Applied fix in the working tree.

• The exact Windows titlebar button frames now occlude the ancestor draggable titlebar hitbox, so clicks remain client button input instead of being classified as non-client drag input.
• Covered Tips, Resources, Git, Actions, Open In, and the conditional Prompt Editor/Exit Focus controls.
• No overlays, overlapping interactive frames, hit-test overrides, or synthetic event routing were added.
• macOS/Linux behavior is unchanged.

Final static verifier: PASS.

Per request, no tests, builds, app launch, commit, or push were performed.