feat(db): add checked metadata preparation

[sanohiro]

Summary

• add deterministic checked-metadata regeneration and canonical publication for SQLite and PostgreSQL
• add alignc db prepare, native schema description, exact schema/server identities, and offline whole/per-unit consumption
• serialize publication generations with a persistent operational lock and keep normal builds free of database/environment access
• add required PostgreSQL 16.4 CI plus Q3 codec, migration, native, publication, and stale-evidence owners

Why

Q3 closes the checked/offline pkg.db capability across producer, codec, native database, filesystem publication, and compiler consumer boundaries. CheckedRequired descriptors now have reproducible repository evidence instead of a dormant contract.

The review cycle also closed ambient libpq target selection, cross-statement schema drift, mixed metadata generations, prepare/runtime static-option drift, logical/native parameter pairing, and zero-column Query handling.

Impact

Developers can explicitly regenerate or check SQLite/PostgreSQL metadata with alignc db prepare. Normal check and build consume only canonical .align-db files and never contact a database. PostgreSQL preparation requires a complete URL supplied through a non-PG* environment variable and rejects ambient PG* configuration.

Validation

• scripts/cargo.sh test -p align_driver --test pkg_db_q3 -- --nocapture (14 passed locally; PostgreSQL native case is required, non-skippable CI)
• scripts/cargo.sh test -p align_driver --lib static_inputs::tests::metadata_publication_lock_closes_first_publish_and_overlap_races -- --exact
• scripts/cargo.sh check -p align_driver --lib --bin alignc
• scripts/cargo.sh clippy -p align_driver --lib --bin alignc --test pkg_db_q3 -- -D warnings
• scripts/pre-pr.sh ... (Q3 owner, repository PR gate, workspace lib/bin Clippy)
• host-native full-diff review with all findings fixed in follow-up commits