feat add remote hand tracking backend

package.json

@@ -5,6 +5,8 @@
   "type": "module",
   "scripts": {
     "dev": "vite",
+    "dev:hand": "python3 -m backend.main",
+    "dev:full": "concurrently \"npm run dev\" \"npm run dev:hand\"",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
     "lint:fix": "eslint . --fix",
@@ -31,6 +33,7 @@
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.1",
+    "concurrently": "^9.2.1",
     "eslint": "^9.39.4",
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-prettier": "^5.5.5",