perf: reduce Gunicorn workers to 1 for stability

- Change from 4 workers to 1 worker in both Dockerfile and docker-compose.yml
- Helps reduce resource usage and connection reset issues
- Better for single-user or low-traffic deployment scenarios

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

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

docker-compose.yml

@@ -9,7 +9,7 @@ services:
     environment:
       - FLASK_APP=main.py
       - FLASK_ENV=production
-      - GUNICORN_CMD_ARGS=--workers=4 --bind=0.0.0.0:5000 --timeout=120 --keep-alive=5 --worker-class=sync --worker-connections=1000 --max-requests=1000 --max-requests-jitter=50
+      - GUNICORN_CMD_ARGS=--workers=1 --bind=0.0.0.0:5000 --timeout=120 --keep-alive=5 --worker-class=sync --worker-connections=1000 --max-requests=1000 --max-requests-jitter=50
       # Application configuration
       - UPLOAD_FOLDER=app/static/uploads
       - DATABASE_PATH=pet_pictures.db