Docs mobile nav drawer: focus trap and scroll lock

Severity: Medium Area: Docs / accessibility

The slide-over in DocsShell sets role="dialog" and aria-modal="true" but does not trap focus, restore focus on close, or lock body scroll.

Keyboard and screen-reader users can tab into the page behind the overlay.

Fix: Add focus trap (e.g. focus-trap-react or equivalent), returnFocus, and overflow: hidden on body while open.