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

backend/libs/handlers/app.go

@@ -44,6 +44,7 @@ func (a *App) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("GET /d/{boxID}/f/{fileID}", a.DownloadFile)
 	mux.HandleFunc("GET /d/{boxID}/f/{fileID}/download", a.DownloadFileContent)
 	mux.HandleFunc("GET /d/{boxID}/thumb/{fileID}", a.Thumbnail)
+	mux.HandleFunc("GET /health", a.Health)
 	mux.HandleFunc("GET /healthz", a.Health)
 	mux.HandleFunc("GET /api/v1/health", a.Health)
 	mux.HandleFunc("GET /api/v1/sharex/warpbox-anonymous.sxcu", a.ShareXAnonymousConfig)