feat(docker): Add Docker containerization for React frontend

- Add production compose.yml using published ghcr.io images
- Rename compose.yml to compose.dev.yml for development
- Create config.example.toml configuration template
- Update README.md with Docker setup instructions
- Use ./data directory for configuration and database storage
- Separate development and production Docker workflows

compose.dev.yml

@@ -0,0 +1,25 @@
+services:
+  # React frontend service
+  frontend:
+    build:
+      context: ./frontend
+      dockerfile: Dockerfile
+    restart: "unless-stopped"
+    ports:
+      - "127.0.0.1:3000:80"
+    environment:
+      - API_BACKEND_URL=${API_BACKEND_URL:-http://leggend:8000}
+    depends_on:
+      leggend:
+        condition: service_healthy
+
+  # FastAPI backend service
+  leggend:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    restart: "unless-stopped"
+    ports:
+      - "127.0.0.1:8000:8000"
+    volumes:
+      - "./data:/root/.config/leggen"