[amesk]

Summary

• Add a contextual launch action to the enlarged screenshot viewer in the React landing page.
• Guest OS screenshots launch their QuickBoot scenario; Instant Run and Games restore the corresponding saved machine state.
• Add the same one-click action to the classic root index.html, reusing the exact Run/Play/Teleport link from the selected gallery card.
• Keep ordinary screenshots view-only when no launch target exists.
• Document the user-visible change in CHANGELOG.md.

Verification

• Reviewed the launch targets against the existing gallery card actions.
• Automated build/tests have not been run in this environment; please rely on CI and verify Run, Teleport, and Play from the lightbox in both landing implementations.

Dependency / overlap

This PR touches CHANGELOG.md and the React carousel components also changed by #176 (test/0.4.0-polishing). The feature is isolated to the lightbox action, but merge/rebase should be checked after #176 lands.