feat: Add Instance Details ViewModel and UI for managing instance credentials

- Introduced InstanceDetailsViewModel to handle loading and displaying instance-specific credentials.
- Created InstanceDetailsWindow and associated XAML for displaying admin, database, and OAuth2 credentials.
- Updated InstancesViewModel to include command for opening instance details.
- Enhanced SettingsViewModel to manage Bitwarden and Xibo Bootstrap configurations, including connection testing.
- Added UI components for Bitwarden Secrets Manager and Xibo Bootstrap OAuth2 settings in the SettingsView.
- Implemented password visibility toggles and clipboard copy functionality for sensitive information.

OTSSignsOrchestrator.Desktop/Views/InstancesView.axaml

@@ -16,6 +16,9 @@
             <Grid ColumnDefinitions="*,Auto">
                 <StackPanel Orientation="Horizontal" Spacing="8">
                     <Button Content="Refresh" Command="{Binding LoadInstancesCommand}" />
+                    <Button Content="Details" Classes="accent" Command="{Binding OpenDetailsCommand}"
+                            IsEnabled="{Binding !IsBusy}"
+                            ToolTip.Tip="View credentials and manage this instance." />
                     <Button Content="Inspect" Command="{Binding InspectInstanceCommand}" />
                     <Button Content="Delete" Classes="danger" Command="{Binding DeleteInstanceCommand}" />
                     <Border Width="1" Background="{StaticResource BorderSubtleBrush}" Margin="4,2" />