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>

nginx-site.conf

@@ -0,0 +1,28 @@
+server {
+    listen 80;
+    server_name localhost;
+
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Enable gzip compression
+    gzip on;
+    gzip_types text/css application/javascript image/jpeg image/png;
+    gzip_min_length 1000;
+
+    # Cache static assets
+    location ~* \.(jpg|jpeg|png|gif|ico|css|js)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Main location
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+}