feat: switch GitHub Actions to build optimized Docker image by default

- Change main build to use Dockerfile.optimized (targets ~200MB image)
- Add separate 'full' build job for development variant (2.6GB)
- Update tagging strategy: 'latest' for optimized, 'full' suffix for full variant
- Update documentation to reflect dual image strategy
- Update docker-compose.yml with variant selection comment

This provides users with two options:
- Optimized (default): Pre-built database, minimal size, for production
- Full: Complete n8n packages, dynamic scanning, for development

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

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

README.md

@@ -65,7 +65,9 @@ npm run test-nodes
 
 ## Docker Quick Start 🐳
 
-The easiest way to get started is using Docker:
+The easiest way to get started is using Docker. We provide two image variants:
+- **Optimized** (`latest`): ~200MB, pre-built database, recommended for production
+- **Full** (`full`): 2.6GB, includes n8n packages, for development/dynamic scanning
 
 ### Option 1: Simple HTTP Server (Recommended)