Fix capture overlays in remote display clients

[BenjaminD2023]

Summary

• Make screenshot, recording, and Smart Element selection windows visible to remote-display capture clients.
• Hide shareable screenshot overlays around Snapzy snapshots; keep recording overlays out through the existing explicit window filters and dismiss Smart Element overlays before capture.
• Reuse the existing high-contrast selection cursor for recording-region reselection.
• Add window-sharing regression coverage and update capture documentation.

Validation

• 18 focused tests passed for overlay sharing, live mouse-up snapshots, and Smart Element capture.
• Verified through Continuum that screenshot dimming/selection, recording preflight dimming/selection/toolbar, and Smart Element highlights are visible remotely.
• Verified Snapzy screenshots do not include their own selection overlay.

Fixes #212

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[duongductrong]

Hi @BenjaminD2023, thanks for working on this and getting CI green!

To help verify the end-to-end behavior and ensure the UX works smoothly in practice, could you share a short video or GIF demo showing:

1. The selection/capture overlay visible on the remote display client during capture.
2. The final saved capture confirming that the selection overlay itself is not captured.

Having a quick visual demo would make reviewing and merging this much smoother. Thanks!

[duongductrong]

Hi @BenjaminD2023, just following up to check if you've had a chance to record a quick demo or GIF for this? Having a visual walkthrough would really help us verify the behavior and get this reviewed and merged smoothly.

Thanks again for your time and contribution!