Set up Gradle Kotlin project with Ktor, Docker, and CI pipeline

Dockerfile

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+# Stage 1: Build
+FROM eclipse-temurin:25-jdk-alpine AS build
+WORKDIR /app
+COPY . .
+RUN chmod +x gradlew
+RUN ./gradlew shadowJar --no-daemon
+
+# Stage 2: Run
+FROM eclipse-temurin:25-jre-alpine
+WORKDIR /app
+# Wir kopieren das fertige Jar aus der Build-Stage
+COPY --from=build /app/build/libs/*-all.jar app.jar
+EXPOSE 8081
+ENTRYPOINT ["java", "-jar", "app.jar"]