fix(tui): release overlay focus to explicit targets

Add an explicit overlay unfocus target so callers can move input to the editor or another component while overlays remain visible. Align fallback overlay focus with visual focus order and cover blocked replacement release, null targets, and multi-overlay cycling.

packages/tui/src/index.ts

@@ -99,6 +99,7 @@ export {
 	type OverlayHandle,
 	type OverlayMargin,
 	type OverlayOptions,
+	type OverlayUnfocusOptions,
 	type SizeValue,
 	TUI,
 } from "./tui.ts";