build: use distroless base image for new Dockerfile

Dockerfile

@@ -1,28 +1,19 @@
-# ── Stage 1: Build ────────────────────────────────────────────────────────────
 FROM eclipse-temurin:21-jdk-alpine AS build
+
 WORKDIR /app
 
 COPY pom.xml .
 COPY src ./src
 
-# Download dependencies (cached layer), then build
 RUN apk add --no-cache maven && \
     mvn dependency:go-offline -q && \
     mvn package -DskipTests -q
 
-# ── Stage 2: Runtime ──────────────────────────────────────────────────────────
-FROM eclipse-temurin:21-jre-alpine
+FROM gcr.io/distroless/java21-debian12:nonroot
 WORKDIR /app
 
-# Copy the fat JAR from the build stage
 COPY --from=build /app/target/overseerr-webhook-proxy-*.jar app.jar
 
-# The application.yml can be overridden by mounting a file at:
-#   /app/config/application.yml
-VOLUME ["/app/config"]
-
-EXPOSE 8080
-
 ENTRYPOINT ["java", \
   "-Dspring.config.additional-location=optional:file:/app/config/application.yml", \
-  "-jar", "app.jar"]
+  "-jar", "app.jar"]