docs(apple): Add shake-to-report section and note iOS-only support

Add a "Shake to Report" section to the user feedback setup page and update
the `useShakeGesture` config description to note it's iOS-only.

Ref: getsentry/sentry-cocoa#7579

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

Author: antonis

docs/platforms/apple/common/user-feedback/configuration/index.mdx

@@ -18,7 +18,7 @@ The following options can be configured for the integration in `SentryUserFeedba
 | Option                   | Type            | Default | Description                                                                                                                                                |
 | ------------------------ | --------------- | ------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `animations`             | `Bool`          | `true`  | Whether or not to show animations, like for presenting and dismissing the form.                                                                            |
-| `useShakeGesture`        | `Bool`          | `false` | Use a shake gesture to display the form.                                                                                                                   |
+| `useShakeGesture`        | `Bool`          | `false` | Use a shake gesture to display the form. Only supported on iOS; this is a no-op on macOS, tvOS, watchOS, and visionOS.                                     |
 | `showFormForScreenshots` | `Bool`          | `false` | Any time a user takes a screenshot, bring up the form with the screenshot attached.                                                                        |
 | `tags`                   | `[String: Any]` | `nil`   | Tags to set on the feedback event. This is a dictionary where keys are strings and values can be different data types such as `NSNumber`, `NSString`, etc. |
 

docs/platforms/apple/common/user-feedback/index.mdx

@@ -161,6 +161,18 @@ struct SwiftUIApp: App {
 }
 ```
 
+### Shake to Report
+
+You can enable shake-to-report so that shaking the device opens the User Feedback form. This is only supported on iOS.
+
+```swift
+SentrySDK.start { options in
+    options.configureUserFeedback { config in
+        config.useShakeGesture = true
+    }
+}
+```
+
 ### Session Replay
 
 The User Feedback widget integrates seamlessly with Session Replay. When the widget is opened, the Replay SDK buffers up to 30 seconds of the user's session. If feedback is submitted, this replay is sent along with the feedback, allowing you to view both the feedback and the user's actions leading up to the feedback submission.