release: make stable/devel promotion atomic and verifiable

[NikolayS]

Severity

High — final-release artifact integrity.

Problem

The stable/devel split has no committed promotion command or complete checklist. build/transform.sh points to devel/sql/README.md, but that README explains development install/layout, not how to stamp and promote a release.

CI fully tests devel/sql, while stable smoke covers only sql/pgque.sql plus the plain uninstall. A final prep PR can forget or mismatch sql/pgque-tle.sql, sql/pgque_uninstall.sql, or sql/pgque-tle-uninstall.sql and still pass.

Expected fix

Add an explicit release-validation/promotion path that:

• accepts and validates the release version;
• stamps the development version source and regenerates deterministically;
• promotes exactly the four stable artifacts atomically;
• asserts version/coherence across plain SQL and pg_tle artifacts;
• tests stable install, v0.2 upgrade, pg_tle update/install, and both uninstalls;
• documents tag/release creation and the post-tag return to 0.3.0-devel;
• fails CI on partial or stale stable artifacts.

This should land after the pg_tle update-path decision (#308) and final SQL API shape.