Add Docker support and update README

- Add Dockerfile with multi-stage build for Node.js + React
- Add docker-compose.yml for easy local deployment
- Add .dockerignore to exclude unnecessary files
- Add GitHub Actions workflow for automatic Docker image builds and pushes to GHCR
- Add comprehensive DOCKER.md documentation
- Update README with Docker installation instructions

.dockerignore

@@ -0,0 +1,16 @@
+node_modules
+npm-debug.log
+.git
+.gitignore
+.env
+.DS_Store
+.vscode
+.idea
+*.log
+dist
+build
+coverage
+.next
+out
+client/node_modules
+server/node_modules