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>

Dockerfile

@@ -0,0 +1,16 @@
+FROM nginx:alpine
+
+# Copy website files to nginx html directory
+COPY index.html /usr/share/nginx/html/
+COPY styles.css /usr/share/nginx/html/
+COPY script.js /usr/share/nginx/html/
+COPY logo.png /usr/share/nginx/html/
+
+# Copy custom nginx configuration
+COPY nginx-site.conf /etc/nginx/conf.d/default.conf
+
+# Expose port 80
+EXPOSE 80
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]