Add Dockerfile and Gitea CI/CD workflows

- Dockerfile: eclipse-temurin:25-alpine, exposes port 8080
- build.yml: builds on every branch push with Java 25
- deploy.yml: builds and pushes Docker image on v* tags

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Dockerfile

@@ -0,0 +1,5 @@
+FROM eclipse-temurin:25-alpine
+WORKDIR /app
+ADD ./build/libs/webgit-0.0.1-SNAPSHOT.jar /app/webgit.jar
+ENTRYPOINT ["java", "-jar", "webgit.jar"]
+EXPOSE 8080/tcp