release: prepare 1.5.0 candidate

[omandryk]

Summary

• set the project version and SCM tag metadata for 1.5.0
• finalize the 1.5.0 changelog
• update the README dependency example

Verification

• mvn clean verify -Prelease -Dgpg.skip=true
• 9 tests pass; 7 live-store integration tests remain intentionally skipped
• JAR, sources JAR, and Javadocs JAR build
• public API signatures match 1.4
• isolated Maven repository and blank consumer project resolve and execute 1.5.0

This PR does not publish to Maven Central, create a tag, or create a GitHub Release.