feat: add Docker support and Gitea publish workflow

- Add a multi-stage Dockerfile for building and running the Go backend
- Add .dockerignore to optimize the Docker build context
- Create a Gitea Actions workflow to build and publish Docker images on tag push
- Register a new `/health` endpoint for container healthchecks
- Update README.md with Docker and Podman deployment instructions
- Ignore local `docker-compose.yml` in .gitignore

README.md

@@ -29,6 +29,25 @@ cd backend
 go run ./cmd/warpbox
 ```
 
+## Docker / Podman
+
+Copy the example environment file and adjust values such as `WARPBOX_BASE_URL` and
+`WARPBOX_ADMIN_TOKEN` before running the container:
+
+Copy the example [docker-compose.example.yml](./docker-compose.example.yml) to [docker-compose.yml](./docker-compose.yml), modify as need-be
+
+```bash
+cp .env.example .env
+docker compose -f docker-compose.yml up --build
+```
+
+The compose example also works with Podman compatible compose tools. Its data volume uses
+`./data:/data:Z` for SELinux relabeling, and the container overrides runtime paths to use
+`/data`, `/app/static`, and `/app/templates`.
+
+The image exposes `/health`, `/healthz`, and `/api/v1/health`. Docker and compose healthchecks
+use `/health`.
+
 ## Layout
 
 - `backend/cmd/warpbox` - main application entry point.