feat: Implement HTML-first style preservation system

- Add StyleContext class for extracting and applying HTML attributes/styles
- Enhance MarkdownConverter with style-aware conversion methods
- Switch backend storage from markdown to HTML with 'html' content type
- Update editor workflow to preserve CSS classes, IDs, and attributes
- Maintain markdown editing UX while storing HTML for style preservation
- Support complex attributes like rel, data-*, aria-*, etc.

This enables editing styled content like <a class="fancy" rel="me">text</a>
while preserving all styling attributes through the markdown editing process.

lib/src/core/editor.js

@@ -1,4 +1,5 @@
 import { InsertrFormRenderer } from '../ui/form-renderer.js';
+import { markdownConverter } from '../utils/markdown.js';
 
 /**
  * InsertrEditor - Content editing workflow and business logic
@@ -114,16 +115,35 @@ export class InsertrEditor {
         
         try {
             // Extract content value based on type
-            let contentValue;
+            let markdownContent;
             if (meta.element.tagName.toLowerCase() === 'a') {
                 // For links, save the text content (URL is handled separately if needed)
-                contentValue = formData.text || formData;
+                markdownContent = formData.text || formData;
             } else {
-                contentValue = formData.text || formData;
+                markdownContent = formData.text || formData;
+            }
+            
+            // Convert markdown to HTML with style preservation
+            let contentValue;
+            const contentType = this.determineContentType(meta.element);
+            
+            if (contentType === 'html') {
+                // Extract style context from original element and convert markdown to HTML
+                const { markdown, styleContext } = markdownConverter.htmlToMarkdownWithContext(meta.element.innerHTML, meta.element);
+                
+                if (styleContext && styleContext.hasPreservableContent) {
+                    // Convert markdown back to HTML with style preservation
+                    contentValue = markdownConverter.markdownToHtmlWithStyles(markdownContent, styleContext);
+                } else {
+                    // No styles to preserve, simple conversion
+                    contentValue = markdownConverter.markdownToHtml(markdownContent);
+                }
+            } else {
+                // For other content types (text, link), use markdown as-is
+                contentValue = markdownContent;
             }
             
             // Universal upsert - server handles ID extraction/generation from markup
-            const contentType = this.determineContentType(meta.element);
             const result = await this.apiClient.createContent(
                 contentValue, 
                 contentType, 
@@ -155,8 +175,8 @@ export class InsertrEditor {
             return 'link';
         }
         
-        // ALL text elements use markdown for consistent editing experience
-        return 'markdown';
+        // ALL text elements use HTML storage with markdown editing interface
+        return 'html';
     }
     
     handleCancel(meta) {