docs: ✏️ document onError logic

Author: mjancarik

packages/create-widget/views/preact/template.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "@merkur/preact": "0.39.0"
+    "@merkur/preact": "0.40.0"
   },
   "devDependencies": {
     "@testing-library/jest-dom": "^6.5.0",

packages/create-widget/views/svelte/template.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "@merkur/svelte": "0.39.0"
+    "@merkur/svelte": "0.40.0"
   },
   "devDependencies": {}
 }

packages/create-widget/views/uhtml/template.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "@merkur/uhtml": "0.39.0"
+    "@merkur/uhtml": "0.40.0"
   },
   "devDependencies": {}
 }

website/docs/integration-with-app.md

@@ -288,15 +288,20 @@ return (
 You can also react to component events through callbacks.
 - When widget is mounted, a function passed through `onWidgetMounted` prop is called with the widget instance.
 - Before the widget is unmounted, `onWidgetUnmounting` is called.
-- Whenever error occurs during the widget lifetime, an `onError` function prop is called.
+- Whenever error occurs during the widget lifetime, an `onError` function prop is called. If the `onError` callback returns `true`, the default error fallback will **not** be displayed, allowing you to handle the error with your own custom UI or logic.
 
 ```jsx
 return (
   <MerkurWidget
       widgetProperties={widgetProperties}
       onWidgetMounted={widget => this._widgetMounted()}
       onWidgetUnmouting={widget => this._widgetUnmounting()}
-      onError={error => this._handleError(error)}>
+      onError={error => {
+        console.error('Widget error:', error);
+        // Return true to prevent showing the default error fallback
+        // Return false or undefined to show the default error fallback
+        return this._handleError(error);
+      }}>
     <div>
       Fallback for undefined widgetProperties
     </div>