fix: resolve content update payload parsing and add update vs create logic

- Extract content from formData.content instead of passing whole object
- Add logic to call updateContent() for existing content vs createContent() for new
- Fix 400 Invalid JSON error caused by sending object instead of string
- Handle different formData formats: string, {content: string}, {text: string}

The frontend was sending html_content as {type:'html', content:'...'} object
but server expected a plain string. Now properly extracts the content value.

lib/src/core/editor.js

@@ -113,22 +113,31 @@ export class InsertrEditor {
         console.log('💾 Saving content:', meta.contentId, formData);
         
         try {
-            // Extract content value based on type
+            // Extract content value from formData
             let contentValue;
-            if (meta.element.tagName.toLowerCase() === 'a') {
-                // For links, save the text content (URL is handled separately if needed)
-                contentValue = formData.text || formData;
+            if (typeof formData === 'string') {
+                contentValue = formData;
+            } else if (formData.content) {
+                contentValue = formData.content;
+            } else if (formData.text) {
+                contentValue = formData.text;
             } else {
-                contentValue = formData.text || formData;
+                contentValue = formData;
             }
             
-            // Universal upsert - server handles ID extraction/generation from markup
-            const contentType = this.determineContentType(meta.element);
-            const result = await this.apiClient.createContent(
-                contentValue, 
-                contentType, 
-                meta.htmlMarkup  // Always send HTML markup - server is smart about ID handling
-            );
+            let result;
+            if (meta.contentId) {
+                // Update existing content
+                result = await this.apiClient.updateContent(meta.contentId, contentValue);
+            } else {
+                // Create new content - server handles ID extraction/generation from markup
+                const contentType = this.determineContentType(meta.element);
+                result = await this.apiClient.createContent(
+                    contentValue, 
+                    contentType, 
+                    meta.htmlMarkup  // Always send HTML markup - server is smart about ID handling
+                );
+            }
             
             if (result) {
                 // Store the backend-generated/confirmed ID in the element