fix: Resolve backend logger permission errors

- Fix logger path to use relative path from backend directory
- Add LOG_DIR environment variable support for custom log paths
- Create logs directory with .gitkeep to ensure it exists
- Add docker-entrypoint.sh to handle runtime permissions
- Optimize Dockerfile to set proper permissions for nodejs user
- Ensure logs directory is writable by the application

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

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

backend/src/utils/logger.js

@@ -3,7 +3,7 @@ const DailyRotateFile = require('winston-daily-rotate-file');
 const path = require('path');
 const config = require('../config');
 
-const logDir = path.join(__dirname, '../../../logs');
+const logDir = process.env.LOG_DIR || path.join(__dirname, '../../logs');
 
 // Define log format
 const logFormat = winston.format.combine(