feat: update Docker setup for refactored app structure

- Update Dockerfile to copy new app/ directory structure
- Fix docker-compose.yml volume paths for app/static/uploads
- Add environment variable support for new config system
- Update migration service to use migrate_session_changes.py
- Add .dockerignore for optimized builds
- Remove obsolete version field from docker-compose.yml
- Create comprehensive README_DOCKER.md documentation

The Docker setup now fully supports the refactored Flask application
with modular structure, authentication, and like system.

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

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

docker-compose.yml

@@ -1,17 +1,20 @@
-version: "3.8"
-
 services:
   web:
     build: .
     ports:
       - "54321:5000"
     volumes:
-      - ./static/uploads:/app/static/uploads
+      - ./app/static/uploads:/app/app/static/uploads
       - ./pet_pictures.db:/app/pet_pictures.db
     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
+      # Application configuration
+      - UPLOAD_FOLDER=app/static/uploads
+      - DATABASE_PATH=pet_pictures.db
+      - ADMIN_USERNAME=admin
+      - ADMIN_PASSWORD=password123
     restart: unless-stopped
     healthcheck:
       test:
@@ -36,6 +39,6 @@ services:
     build: .
     volumes:
       - ./pet_pictures.db:/app/pet_pictures.db
-    command: python migrate.py
+    command: python migrate_session_changes.py
     profiles:
       - migrate