a11y: focus trap + initial focus for Settings / Add role / JD triage modals

[telivity-otaip]

Why

Modals (#settings, #addrole, #jdtriage, #ligoogle, legacy #rolepanel) open by toggling .hidden, and Escape already closes some surfaces — but Tab can escape into the page behind, and focus doesn’t always land on the first field.

Size

M — shared helper, wire into open/close paths.

Task

1. Add a tiny focus-trap helper (vanilla JS, no library) used when a .modal opens:
   • move focus into the dialog (first input or close control)
   • cycle Tab / Shift+Tab inside the .box
   • restore focus to the opener on close
2. Ensure each modal has an accessible name (aria-labelledby → existing heading, or aria-label).
3. Keep Escape behavior consistent with today’s close paths.

Acceptance

• Opening Settings / Add role / JD triage moves focus inside the dialog
• Tab does not reach elements under the backdrop while open
• Closing restores focus to the control that opened it
• No new npm dependencies
• npm test passes

Tips

Drawer already has role="dialog" aria-modal="true". Prefer matching that pattern. Avoid rewriting the whole hybrid IA.