docs(sdk): viewport.isVisible and visibility_changed

Author: theqeeqez

apps/docs/packages/telegram-apps-sdk/2-x/components/viewport.md

@@ -110,6 +110,25 @@ if (bindViewportCssVars.isAvailable()) {
 
 :::
 
+## Visibility
+
+To track if mini app is visible, use `isVisible` signal.
+Invisible means app is collapsed or in another tab.
+
+::: code-group
+
+```ts [Variable]
+viewport.isVisible();
+```
+
+```ts [Functions]
+import { isVisible } from '@telegram-apps/sdk';
+
+isVisible()
+```
+
+:::
+
 ## Expanding
 
 To expand the viewport, use the `expand` method.

apps/docs/platform/events.md

@@ -349,6 +349,16 @@ user started dragging the application or called the expansion method.
 > application window. You should probably use a stable height instead of the current one, or handle
 > this problem in another way.
 
+### `visibility_changed`
+
+Available since: **v8.0**
+
+Occurs whenever the mini app is visible or hidden (means collapsed or in another tab).
+
+| Field      | Type      | Description                                        |
+|------------|-----------|----------------------------------------------------|
+| is_visible | `boolean` | Indicates if the application is currently visible. |
+
 ### `write_access_requested`
 
 Available since: **v6.9**