fix: read suspension timestamps in UTC

[RajvardhanPatil07]

Fixes #841.

Summary

• read users.suspendedUntil via JDBC with a UTC Calendar so DB UTC DATETIME values are not shifted by the JVM default timezone
• remove the forced UTC Maven test workaround now that the production reads are timezone-explicit
• add unit coverage for the UTC calendar helper and non-UTC integration coverage for suspended password and SSO authentication

Testing

• git diff --cached --check
• python3 - <<PY ... ET.parse("pom.xml") ... PY
• Not run locally: Maven/Spotless/integration tests, because this machine has no mvn, no Java runtime, and no Docker available.