feat(journal): persist idempotency keys

[bercianor]

Summary

• Add deterministic idempotencyKey derivation for CHANGE_STATE journal events.
• Persist and restore the key in MongoDB, DynamoDB, and SQL without local deduplication.
• Extend focused and nine-dialect SQL coverage.

Verification

• Java 17.0.8-graal focused journal checks: passed.
• SQL runtime matrix (MySQL, SQL Server, Oracle, PostgreSQL, MariaDB, H2, SQLite, Informix, Firebird): 109 tests passed.

Scope

• Couchbase, backfill, paging, and audit compaction are intentionally excluded.