Authorize mailbox admission in the native recipient

[qh-work]

A native recipient can now issue mailbox admission authorization from its registered mailbox and approved incoming contact, then export the original signed destination and current owner status through bounded pages. A Python sender can use those exact originals for actual HTTP admission, retry and recovery. The recipient signs only with its existing identity; this action reserves no new storage and creates no receipt-return grants.

Python and TypeScript share the finite destination journal. Identical retries and cross-client reads return the same bytes, while input conflicts, stale revisions, expired authority and wrong receiver bindings fail. Both clients now authenticate retained mailbox receive statuses inside the signing transaction: revoked parent or storage authority blocks cached and fresh authorization even after the status expires, and remembered document/revision floors remain effective.

Validation: native-issued authorization used for actual sender HTTP admission, lost-reply recovery, Python reopening every exact exported page, offline rejection cases, and expired retained revocation refusing both clients. Package and CI inventories include the new module; the native SDK now contains 69 files. Final-source cloud acceptance remains pending before alpha.0.38 publication. Native source provisioning, sender admission and replica reception are still unfinished.