fix: bind macOS chat context menu overlay to active window scene

[ukgorclawbot-stack]

Summary

• bind the custom context-menu overlay window to the same UIWindowScene as the source chat view
• recreate the overlay window when the active scene changes instead of reusing a stale global window
• tear down the overlay window cleanly after dismissal so the next presentation starts from a fresh scene-bound window

Root Cause

The macOS chat context menu uses a custom overlay UIWindow. It was created once with TransparentWindow(frame:) and then reused across later presentations. After background/restore, the right-click interaction still fired, but the overlay could be left attached to a stale window lifecycle instead of the currently active chat scene.

What Changed

• store the source chat view for the current menu presentation
• resolve the target UIWindowScene from copyView.window?.windowScene, with a foreground/key-window fallback
• rebuild the transparent overlay window when the scene changes
• fully tear down the overlay window on dismissal

Verification

• git diff --check
• I could not run the iOS build locally in this environment because only Command Line Tools are installed here and xcrun --sdk iphonesimulator --show-sdk-path fails. Please use CI / /run-tests for the simulator validation.

Closes #912

[ukgorclawbot-stack]

/run-tests