Use PostgreSQL as the only database backend across runtime, schema tooling, installation, Compose, and CI. Update regression tests and reject removed drivers explicitly.
Introduce aether-data-schema and driver-specific schema generation for Postgres, MySQL, and SQLite.
Split data backends, lifecycle, repositories, and gateway runtime integration across database drivers.
Verified with cargo fmt --all --check, cargo clippy --workspace --all-targets -- -D warnings, and cargo test --workspace.