Refresh demo and add queue screenshot

[tmustier]

Summary

• re-record the multi-message demo with the original GitHub Dark terminal treatment and zoom
• add a high-resolution README screenshot showing 2 steering messages and 3 follow-ups at once
• include the screenshot in the packaged files so the README remains complete outside GitHub

Verification

• npm run ci (30 tests)
• git diff --check
• npm pack --dry-run
• H.264, 1290×700, 30 fps, YUV420p video
• 2579×1400 high-resolution PNG
• compared the video palette with the original v0.1.0 capture: background and panel colours match
• visually reviewed the full video contact sheet, editing states, full-queue frame and final delivery frame

No extension behaviour changes.