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

cmd/serve.go

@@ -141,6 +141,9 @@ func runServe(cmd *cobra.Command, args []string) {
 	// Site enhancement endpoint
 	apiRouter.HandleFunc("/enhance", contentHandler.EnhanceSite).Methods("POST")
 
+	// Static library serving (for demo sites)
+	router.HandleFunc("/insertr.js", contentHandler.ServeInsertrJS).Methods("GET")
+
 	// Handle CORS preflight requests explicitly
 	contentRouter.HandleFunc("/{id}", api.CORSPreflightHandler).Methods("OPTIONS")
 	contentRouter.HandleFunc("", api.CORSPreflightHandler).Methods("OPTIONS")