feat(macos): add 'Check for Updates...' menu item

[interrobangdev]

Summary

Adds a manual "Check for Updates..." menu item to the macOS app, allowing users to trigger update checks on demand.

Fixes #4550

Changes

Swift (AppDelegate.swift)

• Added updateChannel for Flutter communication
• Added checkForUpdates: IBAction triggered by menu
• Added setupUpdateChannel() to lazily initialize the method channel

XIB (MainMenu.xib)

• Added "Check for Updates..." menu item after "About" separator
• Wired to checkForUpdates: selector on AppDelegate

Dart (desktop_update_service.dart)

• Added MethodChannel('com.omi/updates')
• Added _handleMethodCall to receive native calls and trigger checkForUpdates()

Testing

• Menu item appears under Omi menu after "About Omi"
• Clicking triggers Sparkle update check dialog
• Works when app is up to date (shows "up to date" message)
• Works when update is available (shows update dialog)

Screenshots

(Menu item location: Omi > Check for Updates...)

[gemini-code-assist]

Code Review

The pull request successfully adds a 'Check for Updates...' menu item to the macOS application, integrating it with the Flutter update service. The changes involve setting up a Flutter MethodChannel in both Swift and Dart to facilitate communication between the native macOS menu and the Flutter update logic. The XIB file is correctly updated to include the new menu item and wire it to the AppDelegate's action. The overall implementation is clear and follows standard patterns for Flutter-native integration.

[gemini-code-assist]

The setupUpdateChannel method relies on finding the MainFlutterWindow and its FlutterViewController at the time it's called. While this might work in most cases, there's a potential for the updateChannel to remain nil if the main window or its content view controller isn't fully initialized or available when the menu item is first clicked. This could lead to the 'Check for Updates' functionality not working as expected. Consider initializing the updateChannel earlier in the app lifecycle, perhaps in applicationDidFinishLaunching, to ensure it's always ready when needed, or add more robust error handling/retries if the window is not found.

    private func setupUpdateChannel() {
        guard updateChannel == nil else { return }
        
        // Attempt to get the FlutterViewController from the main window
        // A more robust approach might involve storing a direct reference to the FlutterViewController
        // during its initial setup, or ensuring this method is called only after the Flutter engine is fully ready.
        if let mainWindow = NSApp.windows.first(where: { $0 is MainFlutterWindow }) as? MainFlutterWindow,
           let flutterViewController = mainWindow.contentViewController as? FlutterViewController {
            updateChannel = FlutterMethodChannel(
                name: "com.omi/updates",
                binaryMessenger: flutterViewController.engine.binaryMessenger
            )
            NSLog("DEBUG: Created updates method channel")
        } else {
            NSLog("ERROR: Could not find MainFlutterWindow or FlutterViewController to set up update channel.")
        }
    }