Add db-migrations-flyway-liquibase: Flyway vs Liquibase migrations, rollbacks and baselines on Spring Boot 4.1

Companion code for the Flyway vs Liquibase article: checksum validation, out-of-order
and repeatable migrations, baselining an existing schema, Flyway Community's undo/diff/deploy
stubs, concurrent-startup locking for both tools, Liquibase changeset identity and rollback
(auto-generated vs explicit), a verified Liquibase 5.0.3 filename-caching defect, the new
OSS license service, the FSL license change, and running both tools against one database.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Q6XdRjtsp4862EM44T7i9a

db-migrations-flyway-liquibase/docs/output/12-liquibase-rollback-explicit.txt

@@ -0,0 +1,16 @@
+===================================================================
+Liquibase: the same insert, now with an explicit rollback block
+===================================================================
+captured: 2026-09-15T07:07:16.370040970Z
+
+
+-- audit_log right after update() --
+ID | EVENT       
+---+-------------
+1  | system-start
+(1 row)
+
+-- audit_log after rollback(1) — table still exists, the row is gone --
+ID | EVENT
+---+------
+(0 rows)