feat: implement auto-injection of insertr.js with site-specific configuration

• Add /insertr.js endpoint to serve JavaScript library from API server
• Implement demo gate auto-injection for sites without existing gates
• Add dynamic site ID injection using per-demo configuration files
• Fix CORS middleware to support localhost origins on any port
• Update demo commands to use individual insertr.yaml configs
• Resolve content persistence issues by matching site IDs between injection and enhancement
• Enable complete edit/save workflow for demo sites with proper namespace isolation

insertr.yaml

@@ -33,6 +33,7 @@ server:
 cli:
   site_id: "demo"       # Default site ID for CLI operations
   output: "./dist"      # Default output directory for enhanced files
+  inject_demo_gate: true  # Inject demo gate in development mode if no gates exist
   
 # API client configuration (for CLI remote mode)
 api: