Add Maven Wrapper (`mvnw`) for consistent builds**

[RonaldRonnie]

Description:

The project has no Maven Wrapper (mvnw, .mvn/). Contributors must install Maven themselves; CI and “run locally” instructions assume mvn is on the PATH. The Dockerfile was updated to use a Maven image, but local and CI builds would benefit from a wrapper.

Acceptance criteria:

• Add Maven Wrapper to the repo (mvnw, mvnw.cmd, .mvn/)
• README and scripts use ./mvnw (or mvnw.cmd on Windows) where appropriate
• .gitignore does not exclude the wrapper scripts or .mvn (except optional files like .mvn/timing.properties if desired)