[bug] iOS dialog (message/confirm/ask) not working on physical devices in release builds

### Describe the problem

On iOS physical devices, **message**, **confirm**, and **ask** dialogs from `@tauri-apps/plugin-dialog` do not appear in **release builds**, though they work correctly in:
- ✅ Development builds on physical devices
- ✅ iOS Simulator (both dev and release builds)

The issue appears to be related to how the plugin obtains the view controller. The root cause is that `manager.viewController` returns `nil` in release builds on physical devices.

**Symptoms:**
- Dialog methods (`message()`, `confirm()`, `ask()`) are called but no dialog appears
- No error messages in console
- Promise hangs indefinitely (never resolves)
- App becomes unresponsive waiting for dialog response

**Reproduction:**
1. Build the app for iOS in **release mode**
2. Deploy to a **physical iOS device** (iPhone/iPad)
3. Call any dialog function:
import { message } from '@tauri-apps/plugin-dialog';
await message('Test message', { title: 'Test' });
4. Observe that no dialog appears and the promise never resolves

**Environment:**
- iOS: 15.7.9 (and likely other versions)
- Tauri: 2.9.4
- Plugin version: `@tauri-apps/plugin-dialog` latest
- Device: Physical iPhone (not simulator)
- Build type: Release only (dev builds work fine)

#### Describe the solution you'd like
The plugin should use `UIApplication.shared.connectedScenes` to obtain the root view controller instead of relying on `manager.viewController`, which is `nil` in release builds.

#### Proposed fix (Swift):
```
private func getRootViewController() -> UIViewController? {
guard let scene = UIApplication.shared.connectedScenes.first as? UIWindowScene else {
return nil
}

let window = scene.windows.first(where: { $0.isKeyWindow }) ?? scene.windows.first
return window?.rootViewController
}
```
This approach:
- ✅ Works reliably in all iOS configurations (dev/release, simulator/device)
- ✅ Uses modern iOS scene-based architecture (iOS 13+)
- ✅ Properly handles multi-window scenarios
- ✅ Returns the active window's root view controller

#### Workaround implemented
We've created a custom plugin for iOS-only that implements this fix. The plugin correctly obtains the view controller using `UIApplication.shared.connectedScenes` and works in all configurations.
##### Key differences from original plugin:
1. View Controller Access:
- ❌ Original: Uses manager.viewController (returns nil in release builds)
- ✅ Workaround: Uses UIApplication.shared.connectedScenes (always works)
2. Implementation:
```
DispatchQueue.main.async { [weak self] in
guard let rootVC = self?.getRootViewController() else {
invoke.reject("Root view controller not found")
return
}

let alert = UIAlertController(...)
rootVC.present(alert, animated: true)
}
```
The fix is straightforward and only requires changing how the view controller is obtained.

#### Related
This issue is specific to message/confirm/ask dialogs, distinct from file picker issues like #3030.
##### Additional context:
- Safari Web Inspector shows request sent but no response received
- Network layer works correctly (IPC is functional)
- Issue is purely in the Swift/iOS native layer

Would appreciate if this fix could be incorporated into the official plugin to benefit all Tauri iOS developers facing this issue!