fix(ci): properly cache dependencies in Docker layer for GHA cache

[MaxAnderson95]

Summary

Fixes build caching so Maven and npm dependencies are not re-downloaded on every build.

Root Causes Fixed

1. pom.xml was modified before Docker build - The workflow ran ./mvnw versions:set on the runner, modifying pom.xml before sending it to Docker. Since version changed each build, the Docker layer cache was invalidated every time.

2. BuildKit cache mounts are ephemeral - The --mount=type=cache syntax only persists within the BuildKit daemon, which is destroyed after each GHA run. The type=gha cache backend caches Docker layers only, NOT cache mount contents.

Changes

• Remove setup-java and setup-node steps (no longer needed)
• Remove pre-build version modification steps
• Pass VERSION as Docker build-arg instead
• Remove BuildKit cache mounts from all Dockerfiles
• Store dependencies in Docker layer (properly cached by GHA)
• Change npm install to npm ci for faster CI builds

How Caching Now Works

Build 1 (v1.0.0):
  pom.xml (0.0.0-dev) → COPY → creates layer (cache miss)
  mvn dependency:go-offline → RUN → creates layer with deps (cache miss)
  src/ → COPY → creates layer
  mvn versions:set + package → RUN → builds v1.0.0

Build 2 (v1.0.1, same dependencies):
  pom.xml (0.0.0-dev) → COPY → CACHE HIT (same content!)
  mvn dependency:go-offline → RUN → CACHE HIT (no download needed!)
  src/ → COPY → HIT or MISS depending on source changes
  mvn versions:set + package → RUN → builds v1.0.1 (only this runs)