fix: Resolve Docker permission issues in development environment

- Create dedicated Dockerfile.backend.dev for development with proper permissions
- Set user UID/GID to 1000 (common for development systems)
- Create logs and temp directories in Dockerfile before switching user
- Use named volumes for logs, temp, and node_modules to maintain permissions
- Mount only source files instead of entire backend directory
- Remove complex entrypoint script in favor of simple CMD
- Add LOG_DIR and TEMP_DIR environment variables

This fixes the "Permission denied" errors when creating directories in Docker.

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

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

backend/docker-entrypoint.sh

@@ -1,15 +1,5 @@
 #!/bin/sh
 set -e
 
-# Ensure logs directory exists with correct permissions
-if [ ! -d "/app/logs" ]; then
-    mkdir -p /app/logs
-fi
-
-# Ensure temp directory exists
-if [ ! -d "/app/temp" ]; then
-    mkdir -p /app/temp
-fi
-
 # Start the application
-exec node src/app.js
+exec "$@"