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>

docker/Dockerfile.backend.dev

@@ -18,8 +18,9 @@ RUN addgroup -g 1000 -S nodejs && \
 # Copy package files
 COPY package*.json ./
 
-# Install dependencies as root
-RUN npm install
+# Install all dependencies (including devDependencies for development)
+# Make sure NODE_ENV is not set to production during install
+RUN NODE_ENV=development npm install
 
 # Create necessary directories
 RUN mkdir -p logs temp && \
@@ -34,6 +35,9 @@ RUN chown -R nodejs:nodejs /app
 # Switch to non-root user
 USER nodejs
 
+# Set development environment
+ENV NODE_ENV=development
+
 # Expose port
 EXPOSE 7510