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

etc/Model/Config/Backend/HtmlArraySerialized.php

@@ -0,0 +1,32 @@
+<?php
+namespace Shopkeeper\VendorNotes\Model\Config\Backend;
+
+use Magento\Config\Model\Config\Backend\Serialized\ArraySerialized;
+
+class HtmlArraySerialized extends ArraySerialized
+{
+    /**
+     * Process data before saving
+     * Prevent HTML from being escaped in note fields
+     *
+     * @return $this
+     */
+    public function beforeSave()
+    {
+        $value = $this->getValue();
+        
+        if (is_array($value)) {
+            // Don't escape HTML in the note field
+            foreach ($value as &$row) {
+                if (isset($row['note'])) {
+                    // Decode any previously encoded HTML entities
+                    $row['note'] = html_entity_decode($row['note'], ENT_QUOTES, 'UTF-8');
+                }
+            }
+            unset($row);
+        }
+        
+        $this->setValue($value);
+        return parent::beforeSave();
+    }
+}