feat(react-headless-components-preview): add focustrap

[mainframev]

Previous Behavior

Popover had no focus trap. The surface rendered as a <div popover="auto"> and relied entirely on the browser's light-dismiss (Escape, click-outside, popover-stack peer dismissal).

New Behavior

Adds a trapFocus prop on Popover that delegates modal behavior. The surface always renders as a single element; the show mode is wired in usePopover:

• trapFocus={false} (default) — surface.showPopover(). Browser owns light dismiss; no focus trap or autofocus. Explicit role="group" overrides the dialog's implicit role="dialog" so assistive tech
  doesn't announce modal semantics that aren't present.
• trapFocus={true} — surface.showModal(). The platform supplies the focus trap, autofocus, trigger-restoration on close, and inert background — all spec-mandated by . The explicit role is
  dropped so the implicit role="dialog" + aria-modal="true" apply. The cancel event is intercepted (preventDefault + close via onOpenChange) so Escape flows through the same React state path as any other
  dismiss.

A single element supporting both modes means consumers flip one prop instead of swapping component variants, and there's no portal/stacking-context divergence between the two paths.

[github-actions]

📊 Bundle size report

Package & Exports	Baseline (minified/GZIP)	PR	Change
react-headless-components-preview react-headless-components-preview: entire library	107.577 kB 31.646 kB	107.958 kB 31.776 kB	381 B 130 B

_{🤖 This report was generated against 39041d7c84a1e8cca8b74703ddef48b1a88e1a0c}

[github-actions]

Pull request demo site: URL