Add Docker support and improve PDF conversion

Features:
- Dockerfile for containerized deployment
- Docker Compose configuration with health checks
- Automated database initialization via entrypoint script
- Quick start script for easy Docker deployment
- Comprehensive Docker deployment documentation (DOCKER.md)
- Complete README with installation and usage instructions
- .dockerignore for optimized image builds

Improvements:
- PDF conversion now preserves orientation (portrait/landscape)
- PDF rendering at 300 DPI for sharp quality
- Maintains aspect ratio during conversion
- Compact media library view with image thumbnails
- Better media preview with scrollable gallery

Docker Features:
- Multi-stage build for smaller images
- Non-root user for security
- Health checks for container monitoring
- Volume mounts for persistent data
- Production-ready Gunicorn configuration
- Support for Redis caching (optional)

docker-compose.yml

@@ -0,0 +1,32 @@
+version: '3.8'
+
+services:
+  digiserver:
+    build: .
+    container_name: digiserver-v2
+    ports:
+      - "5000:5000"
+    volumes:
+      - ./instance:/app/instance
+      - ./app/static/uploads:/app/app/static/uploads
+    environment:
+      - FLASK_ENV=production
+      - SECRET_KEY=${SECRET_KEY:-your-secret-key-change-this}
+    restart: unless-stopped
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:5000/"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s
+
+  # Optional: Redis for caching (uncomment if needed)
+  # redis:
+  #   image: redis:7-alpine
+  #   container_name: digiserver-redis
+  #   restart: unless-stopped
+  #   volumes:
+  #     - redis-data:/data
+
+# volumes:
+#   redis-data: