Implement portable event deferral and v2 artifacts

[fruwe]

Summary

• implement UML deepest-state handler and deferral precedence, runtime-local ready/deferred mailboxes, FIFO recall, capacity faults, lifecycle disposal, and exact admission identity
• add pure version-2 aggregate, migration, checkpoint, replay, receipt, tombstone, bounded-pruning, public package restore, and transactional host/store operations while preserving version-1 behavior
• preserve and route creation emissions/intents, validate envelopes and checkpoint relationships closed, compare canonical replay digests, and enforce bounded counter validation
• bundle the exact version-2 schemas and update the immutable spec and conformance pins

Review fixes

• address all 18 findings from the independent review of 9aaa045ab20b2c06b41804330fad8f22ff8870e2
• address all 12 follow-up findings from the independent review of 915d03fab9ba3172addf6f2b519b7908a0b929fa
• validate and byte-normalize every admitted/restored mailbox payload against its resolved declaration, enforce event-specific runtime/system provenance, and validate the creation result digest against the revision-zero aggregate
• return mandatory ordered migration audit records from the public v2 migration operation and retain exact transactional host audit persistence
• make empty-route v2 host maintenance migration commit successfully with consistent internal disposal evidence
• enforce converted legacy delivery origin, mailbox labeling, wrapped producer reference, allocation, processed-terminal provenance, and global retained allocation ownership during checkpoint restore
• update present-tense repository guidance to the authoritative pins and current suite counts
• keep the conformance driver delegated to the public implementation without expected-result passthrough, error rewriting, expected-valid suppression, or skipped comparison

Validation

• ruff check .: passed
• mypy src/determa: passed (25 source files)
• complete unit suite: 332 passed, 5 skipped
• host/store transaction suite: 104 passed
• exact all-vector conformance: 532 passed, including all 106 version-2 vectors

Authoritative pins

• spec: 2e33036563cb966b07124197db672159b4b7e1f4
• conformance: 531468c59c7a2dc32f5cbe92cfabf89805d27f6a

Closes #82