Simplify script injection to single script with data attribute configuration

- Replace dual script injection (external + inline) with single script approach
- Pass site configuration via data attributes instead of inline JavaScript
- Update library auto-initialization to read config from script data attributes
- Reduce HTML bloat by eliminating 30+ lines of inline initialization code
- Maintain future-proof CDN compatibility and duplication prevention

Enhanced files now contain only one clean script tag with configuration.

test-sites/demo-site/insertr.js

@@ -4104,7 +4104,18 @@ Please report this to https://github.com/markedjs/marked.`,e){let r="<p>An error
     // Auto-initialize in development mode with proper DOM ready handling
     function autoInitialize() {
         if (document.querySelector('.insertr')) {
-            window.Insertr.init();
+            // Check for configuration from script data attributes
+            const insertrScript = document.querySelector('script[data-insertr-injected]');
+            const config = {};
+            
+            if (insertrScript) {
+                config.siteId = insertrScript.getAttribute('data-site-id') || 'demo';
+                config.apiEndpoint = insertrScript.getAttribute('data-api-endpoint') || '/api/content';
+                config.mockAuth = insertrScript.getAttribute('data-mock-auth') === 'true';
+                config.debug = insertrScript.getAttribute('data-debug') === 'true';
+            }
+            
+            window.Insertr.init(config);
         }
     }