fix: cross-Boot-version autoconfiguration and CI-friendly version resolution

- OrdoJdbcAutoConfiguration: use string-based @AutoConfigureAfter(name = ...)
  to reference both Spring Boot 3.x and 4.x DataSource/Flyway autoconfiguration
  classes, since Boot 4 relocated these to dedicated modules.
- flatten-maven-plugin: switch flattenMode from resolveCiFriendliesOnly to
  defaults so inter-module dependency versions are fully resolved (not just
  the project's own <version>) when installed, fixing dependency resolution
  for external consumers.
- Align sibling-module dependency versions to use \ consistently.
- Ignore generated .flattened-pom.xml files.

.gitignore

@@ -3,6 +3,7 @@ target/
 !**/src/main/**/target/
 !**/src/test/**/target/
 .kotlin
+.flattened-pom.xml
 
 ### IntelliJ IDEA ###
 .idea/modules.xml