Upgrade application baseline to Java 25

[alexlang74]

Summary

• move Maven compiler configuration from Java 8 source/target to Java release 25
• modernize build plugins (compiler/war/resources/dependency/enforcer) and upgrade liberty-maven-plugin
• add Maven Enforcer rules for Maven and Java version requirements
• upgrade Derby dependency to 10.17.1.0 and update Derby jar references in Liberty and Docker config
• pin Liberty container images to Java 25 capable tags for both Derby and DB2 Dockerfiles
• update README files with Java 25 and Maven prerequisites

Validation completed in this branch

• mvn clean package -DskipTests on JDK 25: ✅ success
• mvn liberty:run + HTTP check http://localhost:9080/daytrader/: ✅ HTTP 200
• mvn liberty:stop: ✅ success

Validation not completed in this agent environment

• Docker image builds for Dockerfile and Dockerfile-db2: ⚠️ skipped (docker CLI not installed in cloud environment)

Notes

• this change intentionally keeps Java EE 8 (javax.*) APIs and Liberty feature levels unchanged to avoid mixing Java upgrade with Jakarta namespace migration.