feat: Add initial frontend dependencies, base CSS, and Gitea Docker build workflow.

backend/Dockerfile

@@ -0,0 +1,13 @@
+# Build stage
+FROM maven:3.9.12-eclipse-temurin-25 AS build
+WORKDIR /app
+COPY pom.xml .
+COPY src ./src
+RUN mvn clean package -DskipTests
+
+# Run stage
+FROM eclipse-temurin:25-jre
+WORKDIR /app
+COPY --from=build /app/target/*.jar app.jar
+EXPOSE 8080
+ENTRYPOINT ["java", "-jar", "app.jar"]