fix: Use built-in node user to avoid GID conflicts

- Remove custom nodejs user creation that was causing GID 1000 conflicts
- Use the built-in 'node' user from node:alpine image
- Update volume mount path from /home/nodejs to /home/node
- Simplify Dockerfile by removing unnecessary user creation

This fixes the "addgroup: gid '1000' in use" error during Docker build.

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

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

docker/Dockerfile.backend.dev

@@ -11,10 +11,6 @@ RUN apk add --no-cache bash
 # Create app directory
 WORKDIR /app
 
-# Create non-root user (same UID/GID as most development systems)
-RUN addgroup -g 1000 -S nodejs && \
-    adduser -S nodejs -u 1000 -G nodejs
-
 # Copy package files
 COPY package*.json ./
 
@@ -29,11 +25,11 @@ RUN mkdir -p logs temp && \
 # Copy application files
 COPY . .
 
-# Change ownership of everything to nodejs user
-RUN chown -R nodejs:nodejs /app
+# Change ownership of everything to node user (built-in)
+RUN chown -R node:node /app
 
 # Switch to non-root user
-USER nodejs
+USER node
 
 # Set development environment
 ENV NODE_ENV=development