onejs-ui: in-menu keyboard navigation for Select / DropdownMenu

[Singtaa]

Summary

onejs-ui's Select and DropdownMenu are currently pointer-driven: the menu opens, flips/shifts, and dismisses on outside-press or Escape, but in-menu keyboard navigation is not wired — you can't arrow through the options or Enter to choose with the keyboard once the menu is open.

This is the in-menu nav follow-up; it's distinct from the focus-visible ring work (the menu trigger already participates in the focus-visible system).

Desired behavior

When an open Select / DropdownMenu has focus:

• Up/Down (and gamepad d-pad) move an active/highlighted option, wrapping at the ends.
• Enter / Space commit the highlighted option (and close).
• Escape closes without committing (already works).
• Highlight uses the same focus-visible ring treatment as the rest of the library.

Notes

• Files: JSModules/onejs-ui/src/components/Select/Select.tsx, .../DropdownMenu/DropdownMenu.tsx.
• The menu is portaled/anchored, so it should establish a FocusScope (autofocus the active item, trap, restore to the trigger on close) and drive option focus via the existing focus utilities.
• Replaces an earlier incorrect in-code reference to Runtime focus: pointer↔navigation focus desync corrupts the focus ring (UI Toolkit + Input System) #108 (which is an unrelated, closed focus-ring-desync issue); the code comments now point here.