fix: add missing patch method to APIClient

Added PATCH request method to the shared APIClient class. The method
was missing which caused "apiClient.patch is not a function" error
when saving product edits on the vendor-product-edit page.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/shared/js/api-client.js

@@ -221,6 +221,21 @@ class APIClient {
         });
     }
 
+    /**
+     * PATCH request
+     */
+    async patch(endpoint, data = {}) {
+        apiLog.debug('PATCH request data:', {
+            hasData: !!data,
+            dataKeys: Object.keys(data)
+        });
+
+        return this.request(endpoint, {
+            method: 'PATCH',
+            body: JSON.stringify(data)
+        });
+    }
+
     /**
      * DELETE request
      */