fix: Resolve nodemon not found error in development Docker

- Explicitly set NODE_ENV=development during npm install to include devDependencies
- Add NODE_ENV=development environment variable in Dockerfile
- Add fallback dev:node script using Node.js --watch flag
- Ensure nodemon is installed with other development dependencies

This fixes the "sh: nodemon: not found" error in the development container.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/package.json

@@ -6,6 +6,7 @@
   "scripts": {
     "start": "node src/app.js",
     "dev": "nodemon src/app.js",
+    "dev:node": "node --watch src/app.js",
     "test": "jest --coverage",
     "lint": "eslint src/",
     "lint:fix": "eslint src/ --fix"