Release 2026.05.20 jdt2jar fixes JDK 25 bump and helper script

[simbo1905]

Summary

• Bump Docker build stage from JDK 24 to JDK 25 LTS and fix WORKDIR in the distroless stage (Issue Add offline jdt2jar CLI and distroless packaging #148)
• Document docker cp fallback for macOS/Colima and add helper script scripts/jdt2jar.sh for restricted volume mount environments (Issue Add offline jdt2jar CLI and distroless packaging #148)
• Remove accidental tmp test artifacts
• Branch-local version bump to 2026.05.20 for the release branch

This is the release branch rel-2026.05.20; opening as draft so the version bump and remaining scope can be reviewed before merge.

Testing

• Verify jdt2jar docker build and tests: run the jdt2jar module test suite
• Confirm scripts/jdt2jar.sh works in restricted volume mount environments

[simbo1905]

Superseded by a clean fixes branch based on current main; the 2026.05.20 version bump is intentionally excluded.