Private in-memory URL elicitation store used by default.

Each server instance owns an ETS store process by default unless configured with an external store adapter. The in-memory store is bounded by entry and approximate external-term byte limits. It rejects duplicate record keys and never evicts an unexpired approval to admit another one. Periodic cleanup is limited to 1,000 records per call; admission cleanup scans at most the configured entry bound and reclaims as many expired records as the new record needs.