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.Core/Services/InstanceService.cs

@@ -32,6 +32,7 @@ public class InstanceService
     private readonly IDockerSecretsService _secrets;
     private readonly XiboApiService _xibo;
     private readonly SettingsService _settings;
+    private readonly PostInstanceInitService _postInit;
     private readonly DockerOptions _dockerOptions;
     private readonly ILogger<InstanceService> _logger;
 
@@ -44,6 +45,7 @@ public class InstanceService
         IDockerSecretsService secrets,
         XiboApiService xibo,
         SettingsService settings,
+        PostInstanceInitService postInit,
         IOptions<DockerOptions> dockerOptions,
         ILogger<InstanceService> logger)
     {
@@ -55,6 +57,7 @@ public class InstanceService
         _secrets = secrets;
         _xibo = xibo;
         _settings = settings;
+        _postInit = postInit;
         _dockerOptions = dockerOptions.Value;
         _logger = logger;
     }
@@ -255,8 +258,13 @@ public class InstanceService
 
             _logger.LogInformation("Instance created: {StackName} | duration={DurationMs}ms", stackName, sw.ElapsedMilliseconds);
 
+            // ── 8. Post-instance init (fire-and-forget background task) ──────
+            // Waits for Xibo to be ready then creates admin user, OAuth app, and sets theme.
+            var instanceUrl = $"https://{cmsServerName}";
+            _ = Task.Run(async () => await _postInit.RunAsync(abbrev, instanceUrl));
+
             deployResult.ServiceCount = 4;
-            deployResult.Message      = "Instance deployed successfully.";
+            deployResult.Message      = "Instance deployed successfully. Post-install setup is running in background.";
             return deployResult;
         }
         catch (Exception ex)