feat: Add SilverSHELL SDK documentation page with downloadable templates

Added comprehensive SDK page at /sdk with:
- Downloadable SilverSHELL starter template (6.3 KB)
- Downloadable SilverSHELL module template (14 KB)
- Quick start guide with step-by-step instructions
- Creating applications guide (configuration, UI, manual install)
- Creating modules guide with template options
- Publishing modules guide (automated CI/CD + manual)
- Available modules list from library.silverlabs.uk
- Resources and support links

Initial commit includes:
- Complete static website with Docker deployment
- SilverLabs branding and styling
- Nginx configuration for production serving

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

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

.dockerignore

@@ -0,0 +1,5 @@
+docker-compose.yml
+.git
+.gitignore
+*.md
+README.md