Give the research atlas one keyboard topic choice

[aruintelligence]

Change

• Make the four mutually exclusive atlas topics a named radio group with one tab stop, arrow navigation, Home, and End.
• Keep the selected topic, visible labs, and shareable topic hash in sync. Preserve local search text when changing topics; a direct shared hash starts clean.
• Keep a prediction visible if the same challenge condition is reselected; changing conditions still clears it.

Verification

• node --test test/home-atlas-choice.test.js test/home-challenge-selection.test.js test/home-field-choice.test.js test/home-boundary-selection.test.js (4 passed locally).
• Live Pages interaction after merge.

The challenge uses project-authored saved evidence; it is not a human approval, provider call, or delivery test.