Gracefully handle connection error between dashboard and app host

[Copilot]

When the dashboard cannot connect to the app host, RpcExceptions were bubbling up to Blazor's error boundary, displaying the technical yellow error bar instead of providing helpful user guidance.

This change adds graceful error handling to the ApplicationName component, which is one of the first components to establish connection with the app host. Now when connection fails:

Before:

• RpcException bubbles up → Blazor error boundary → Yellow error bar with technical details
• User sees confusing technical error message
• No clear path to recovery

After:

• RpcException caught → User-friendly dialog displayed
• Clear message: "Unable to connect to the app host. Please ensure the app host is running and try again."
• Retry button refreshes the dashboard for immediate recovery
• Cancel button dismisses dialog gracefully

Implementation Details

New ConnectionErrorDialog Component

• Created Components/Dialogs/ConnectionErrorDialog.razor using FluentUI components
• Implements IDialogContentComponent<ConnectionErrorDialogResult> interface
• Provides two actions: Retry (refreshes dashboard) and Cancel (dismisses dialog)

Enhanced ApplicationName Component Error Handling

try
{
    await DashboardClient.WhenConnected.WaitAsync(_disposalCts.Token);
}
catch (RpcException)
{
    // Show user-friendly dialog instead of letting exception bubble up
    await ShowConnectionErrorDialogAsync();
}
catch (Exception)
{
    // Handle other connection-related errors gracefully
    await ShowConnectionErrorDialogAsync();
}

Localized Error Messages

Added new resource strings in Dialogs.resx:

• Connection error dialog title and message
• Retry and cancel button labels
• Properly integrated with existing localization system

Retry Mechanism

The retry button calls NavigationManager.NavigateTo("/", forceLoad: true) to completely refresh the dashboard, allowing all components to re-initialize and attempt connection again.

This provides a much better user experience when the app host is temporarily unavailable or takes time to start up, replacing technical error messages with clear guidance and recovery options.

Fixes #10879.

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[JamesNK]

The dashboard failing to connect to the app host on startup is now the most common unhandled exception. This change handles it more cleanly.

Dialog displayed on startup when the dashboard can't connect:

[davidfowl]

Nice!

[JamesNK]

Hmm, the retry button won't actually do anything. Once the connect TCS is failed then that's it until the dashboard is restarted.

Need to have a method on the client to force it to reconnect.