CNGX_FOCUSABLE_SELECTOR

Description#

CSS selector matching natively-focusable elements: links with an href, the enabled form controls, and anything with an explicit non-negative tabindex. Form controls carry :not(:disabled) because a disabled control is not in the tab order - without it a descendant probe would count a disabled button as focusable and a restore target could land on an unfocusable element. Single source of truth for "is this focusable" - the element-level CngxFocusRestore predicate matches against it, and descendant probes (e.g. "does this panel contain a focusable child?") query against it. Keeping one selector stops the two uses from drifting apart.