ci: add Hugo blog CI/CD to k3s

- Enable Gitea Container Registry
- Dockerfile: nginx:alpine serving hugo public/
- Gitea Actions: build & push image + deploy to k3s
- k8s manifests: namespace hugo, deployment, service, ingress
- RBAC: allow runner to update deployments in hugo ns
- .gitignore: add public/ (CI builds it)

Dockerfile

@@ -0,0 +1,3 @@
+FROM nginx:alpine
+COPY public/ /usr/share/nginx/html
+EXPOSE 80