Fix HTML rendering for vendor notes links

Add proper HTML filtering to render mailto links and formatting in vendor notes.

- Create HtmlArraySerialized backend model to prevent HTML escaping
- Add filterOutputHtml() method to safely render HTML content
- Update template to use HTML filtering
- Decode HTML entities before display

view/adminhtml/templates/order/view/vendor_notes.phtml

@@ -15,7 +15,7 @@ $notes = $block->getVendorNotes();
                             <span class="title"><?php echo __('Vendor Note %1', $index + 1); ?></span>
                         </div>
                         <div class="vendor-note-content" style="padding: 10px 0; line-height: 1.6;">
-                            <?php echo $note; // Output as HTML for links and multi-lines ?>
+                            <?php echo $this->filterOutputHtml($note); ?>
                         </div>
                     </div>
                     <?php if ($index < count($notes) - 1): ?>
@@ -25,4 +25,4 @@ $notes = $block->getVendorNotes();
             </div>
         </div>
     </section>
-<?php endif; ?>
+<?php endif; ?>