createPaginatorAnnouncer

Description#

Builds the paginator live-region message as a single derived signal - no class logic baked into the shell, so the skin still ejects cleanly. The message is a linkedSignal over [pageIndex, totalPages, isBusy] from CNGX_PAGINATOR_HOST: it speaks "Page N of M" on every effective-page change (navigation OR a total-shrink clamp, so the clamp is never silent), "Loading" while busy, and "Updated" on the first settle after busy. Phrasing comes from injectPaginatorConfig.

The previous source value (held by linkedSignal) is what distinguishes a settle from a steady state, so there is no signal write in an effect and no imperative previous tracking. Identical consecutive messages dedupe through the signal's value equality, so the live region never re-announces a no-op.

Must run in an injection context (call as a field initialiser on the shell).