docs: fix svelte app unmount code (#1673)

Author: hyunbinseo

docs/guide/essentials/content-scripts.md

@@ -211,9 +211,7 @@ export default defineContentScript({
       anchor: 'body',
       onMount: (container) => {
         // Create the Svelte app inside the UI container
-        mount(App, {
-          target: container,
-        });
+        return mount(App, { target: container });
       },
       onRemove: (app) => {
         // Destroy the app when the UI is removed
@@ -396,11 +394,9 @@ export default defineContentScript({
       anchor: 'body',
       onMount: (container) => {
         // Create the Svelte app inside the UI container
-        mount(App, {
-          target: container,
-        });
+        return mount(App, { target: container });
       },
-      onRemove: () => {
+      onRemove: (app) => {
         // Destroy the app when the UI is removed
         unmount(app);
       },