produce demo assets for public release

[github-actions]

Summary

Capture high-signal visuals and recordings that demonstrate the CLI flow,
validation output, and work item lifecycle.

Acceptance criteria

• A short terminal recording (asciinema or similar) covers init, new work item,
  and validation.
• At least 2 annotated screenshots or GIFs show the workboard and a work item
  file with front matter.
• Assets are referenced from README and/or public release docs.