feat(tui): add skillsHub overlay state wiring

Extend OverlayState with a skillsHub flag, fold it into $isBlocked, and
teach Ctrl+C to close the overlay so later PRs can render the component
behind this slot.

ui-tui/src/app/interfaces.ts

@@ -57,6 +57,7 @@ export interface OverlayState {
   pager: null | PagerState
   picker: boolean
   secret: null | SecretReq
+  skillsHub: boolean
   sudo: null | SudoReq
 }