chore: add Cloud Agent development environment (JDK 16 + Maven)

[alejouribesanchez]

Summary

Adds a Cursor Cloud Agent development environment for veryfi-java so the repository is usable out of the box (build, tests, coverage).

• .cursor/Dockerfile — based on the official maven:3.8.5-eclipse-temurin-16 image, pinning Eclipse Temurin JDK 16 + Maven 3.8.5, and adding git/curl plus a non-root ubuntu user. JDK 16 matches the project's maven.compiler.target and the JDK used by the GitHub Actions CI. JDK 16 (rather than a newer JDK such as 21) is required because JaCoCo 0.8.7 cannot instrument bytecode produced by newer JDKs.
• .cursor/environment.json — runs as the ubuntu user, builds from the Dockerfile, and uses mvn -B -ntp -DskipTests package as an idempotent install step that warms the Maven local repository and compiles the project.

This is a library SDK with no long-running services, so no start/terminals commands are needed. The end-to-end flow is exercised by the mocked JUnit test suite (141 tests).

Validation

The committed Dockerfile image was built and the full flow was run inside the resulting container (fresh ~/.m2, dependencies pulled from Maven Central):

Check	Result
Image builds from .cursor/Dockerfile	Success
Tool versions in container	JDK 16.0.2 (Temurin), Maven 3.8.5, user ubuntu, JAVA_HOME=/opt/java/openjdk
install (mvn -B -ntp -DskipTests package)	BUILD SUCCESS (main/sources/javadoc jars)
mvn -B -ntp test	141 tests, 0 failures, 0 errors
JaCoCo coverage report	Generated
install idempotence	BUILD SUCCESS on repeated runs