[SandObserver]

Summary

• Return the photographer's name, profile link and the Unsplash link with the photo from /api/wallpaper. The profile link is built from a validated username, with utm_source=stackyard&utm_medium=referral.
• Request the photo's links.download_location once per new photo, with the key, and only on https://api.unsplash.com/.
• Store the credit with the cached wallpaper in the browser. An entry without a credit is refetched.
• Show the credit as "Name / Unsplash" with both links on the dashboard: bottom inline-start on desktop, top centre on phones, moved to the top corner when the Dock leaves too little room.
• Tone the credit from the wallpaper sampling like the icon labels, with the secondary label colour at rest and the primary one on hover or focus.

Testing
All green, including e2e. Added tests for the credit, the download request, the cached credit and the credit placement.

Changelog

Fixed

• Credit the photographer and Unsplash on an Unsplash wallpaper, as Unsplash's API terms require.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.