feat: Add main application views and structure

- Implemented CreateInstanceView for creating new instances.
- Added HostsView for managing SSH hosts with CRUD operations.
- Created InstancesView for displaying and managing instances.
- Developed LogsView for viewing operation logs.
- Introduced SecretsView for managing secrets associated with hosts.
- Established SettingsView for configuring application settings.
- Created MainWindow as the main application window with navigation.
- Added app manifest and configuration files for logging and settings.

OTSSignsOrchestrator.Desktop/ViewModels/MainWindowViewModel.cs

@@ -0,0 +1,60 @@
+using System.Collections.ObjectModel;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace OTSSignsOrchestrator.Desktop.ViewModels;
+
+public partial class MainWindowViewModel : ObservableObject
+{
+    private readonly IServiceProvider _services;
+
+    [ObservableProperty]
+    private ObservableObject? _currentView;
+
+    [ObservableProperty]
+    private string _selectedNav = "Hosts";
+
+    [ObservableProperty]
+    private string _statusMessage = "Ready";
+
+    public ObservableCollection<string> NavItems { get; } = new()
+    {
+        "Hosts",
+        "Instances",
+        "Create Instance",
+        "Secrets",
+        "Settings",
+        "Logs"
+    };
+
+    public MainWindowViewModel(IServiceProvider services)
+    {
+        _services = services;
+        NavigateTo("Hosts");
+    }
+
+    partial void OnSelectedNavChanged(string value)
+    {
+        NavigateTo(value);
+    }
+
+    [RelayCommand]
+    private void NavigateTo(string page)
+    {
+        CurrentView = page switch
+        {
+            "Hosts" => (ObservableObject)_services.GetService(typeof(HostsViewModel))!,
+            "Instances" => (ObservableObject)_services.GetService(typeof(InstancesViewModel))!,
+            "Create Instance" => (ObservableObject)_services.GetService(typeof(CreateInstanceViewModel))!,
+            "Secrets" => (ObservableObject)_services.GetService(typeof(SecretsViewModel))!,
+            "Settings" => (ObservableObject)_services.GetService(typeof(SettingsViewModel))!,
+            "Logs" => (ObservableObject)_services.GetService(typeof(LogsViewModel))!,
+            _ => CurrentView
+        };
+    }
+
+    public void SetStatus(string message)
+    {
+        StatusMessage = message;
+    }
+}