Add Docker support and environment configuration

Introduced Dockerfile, .dockerignore, and example environment file for containerization. Added compose.yml for Docker Compose setup and renamed docker-compose.dev.yml to compose.dev.yml. Updated build.gradle.kts for Java 21 and shadow plugin, and improved .gitignore and .gitattributes. Refactored Config.java to reorder ENV initialization.

Dockerfile

@@ -0,0 +1,19 @@
+FROM amazoncorretto:21.0.5 AS deps
+WORKDIR /build
+COPY --chmod=0755 gradlew gradlew
+COPY gradle/ gradle/
+RUN --mount=type=bind,source=build.gradle.kts,target=build.gradle.kts \
+    --mount=type=cache,target=/root/.gradle \
+    ./gradlew dependencies --no-daemon
+
+FROM deps AS package
+WORKDIR /build
+COPY ./src src/
+RUN --mount=type=bind,source=build.gradle.kts,target=build.gradle.kts \
+    --mount=type=cache,target=/root/.gradle \
+    ./gradlew shadowJar -x test --no-daemon
+RUN cp build/libs/*-all.jar app.jar
+
+FROM amazoncorretto:21.0.5 AS final
+COPY --from=package build/app.jar app.jar
+ENTRYPOINT [ "sh", "-c", "java ${JAVA_OPTS} -jar app.jar" ]