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.

internal/api/handlers.go

@@ -299,13 +299,13 @@ func (h *ContentHandler) CreateContent(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	// Determine content type: use provided type, fallback to existing type, default to "text"
+	// Determine content type: use provided type, fallback to existing type, default to "html"
 	contentType := req.Type
 	if contentType == "" && contentExists {
 		contentType = h.getContentType(existingContent)
 	}
 	if contentType == "" {
-		contentType = "text" // default type for new content
+		contentType = "html" // default type for new content (changed from "text")
 	}
 
 	var content interface{}

internal/engine/injector.go

@@ -103,6 +103,8 @@ func (i *Injector) InjectBulkContent(elements []ElementWithID) error {
 			i.injectTextContent(elem.Element.Node, contentItem.Value)
 		case "markdown":
 			i.injectMarkdownContent(elem.Element.Node, contentItem.Value)
+		case "html":
+			i.injectHTMLContent(elem.Element.Node, contentItem.Value)
 		case "link":
 			i.injectLinkContent(elem.Element.Node, contentItem.Value)
 		default: