feat(sql): persist journal event payloads

[bercianor]

Summary

• Replace flattened SQL audit columns in journal rows with a local JSON payload codec.
• Use portable large-text payload types and dialect-aware JDBC schema validation.
• Preserve journal envelope, ordering, acknowledgement, and CHANGE_STATE-only behavior.

Verification

• SQL mapper and dialect tests with strict TDD evidence.
• Java 17.0.8-graal SQL audit-store matrix across MySQL, SQL Server, Oracle, PostgreSQL, MariaDB, H2, SQLite, Informix, and Firebird.

Scope

This PR contains only PR1 SQL journal payload persistence. The idempotency-key work remains separate WIP and is not included.