Polish task brief labels and README terminal example

[liolevx]

Summary

• Use Relevant files, Related tests, and Checks to run in normal and verbose task briefs; no selection or JSON changes.
• Replace the README illustration with the approved compact image and a short, honest excerpt label.
• Prepare source-install wording for the first npm release.

Validation

• Two new label tests were red before the change and now pass.
• Updated image/caption contract tests; all approved local checks pass.
• Independent read-only review approved; 37 focused checks passed.
• Compiled read-only preview safety and real installed-package lifecycle smoke passed.

No package has been published by this PR.