Add mobile-responsive layout to viz UI

[joe32140]

Summary

• Stack paper/comment panels on mobile (≤768px) with a bottom nav bar to switch between views
• Tapping a highlighted paragraph auto-switches to the Comments panel; tapping a comment card auto-switches to the Paper panel
• Header wraps to two rows on mobile (paper select drops to second row); legend hidden on small screens
• Comment count badge on the mobile nav Comments button
• Extra compact layout at ≤480px (version badge hidden, smaller metrics bar)

Test plan

• Open http://localhost:8080 in desktop browser — layout unchanged
• Open in mobile browser or DevTools device emulator (≤768px) — bottom nav appears, single-panel switching works
• Tap a highlighted paragraph → switches to Comments panel and scrolls to card
• Tap a comment card with a location → switches to Paper panel and scrolls to paragraph
• Switch papers from dropdown → resets to Paper panel on mobile

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