feat: initial landing page with K8s deploy config

- Nginx static serving with APP_URL env var
- K8s manifests for prod and staging
- Gitea Actions CI/CD pipeline

Dockerfile

@@ -0,0 +1,9 @@
+FROM nginx:alpine
+
+ARG APP_URL=https://app.batida.io
+
+COPY index.html /tmp/index.html
+RUN sed -i "s|{{APP_URL}}|${APP_URL}|g" /tmp/index.html
+RUN mv /tmp/index.html /usr/share/nginx/html/index.html
+
+EXPOSE 80