ci: integrate frontend tests into Maven build + Docker

- Add exec-maven-plugin to pom.xml with 3 npm executions:
  * npm-install (initialize phase)
  * frontend-build (generate-resources phase)
  * frontend-test (test phase)
- Add skipFrontend and skipFrontendTests Maven properties
- Dockerfile now runs npm test in frontend stage
- Dockerfile removes -DskipTests and passes -DskipFrontend=true
  to the Maven stage (frontend already built in its own stage)

Dockerfile

@@ -7,6 +7,7 @@ COPY frontend/package.json frontend/package-lock.json ./
 RUN npm ci 2>/dev/null || npm install --legacy-peer-deps
 COPY frontend/ ./
 RUN npm run build
+RUN npm test
 
 # ─── 2. Build Quarkus app ────────────────────────
 FROM maven:3-eclipse-temurin-21-alpine AS build
@@ -15,7 +16,7 @@ COPY pom.xml ./
 COPY src ./src
 # Copy the built frontend into the source tree so maven-resources-plugin picks it up
 COPY --from=frontend /build/dist ./frontend/dist/
-RUN mvn package -DskipTests -q
+RUN mvn package -q -DskipFrontend=true
 
 # ─── 3. Runtime ──────────────────────────────────
 FROM eclipse-temurin:21-jre-alpine