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/Views/MainWindow.axaml

@@ -0,0 +1,62 @@
+<Window xmlns="https://github.com/avaloniaui"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:vm="using:OTSSignsOrchestrator.Desktop.ViewModels"
+        xmlns:views="using:OTSSignsOrchestrator.Desktop.Views"
+        x:Class="OTSSignsOrchestrator.Desktop.Views.MainWindow"
+        x:DataType="vm:MainWindowViewModel"
+        Title="OTS Signs Orchestrator"
+        Width="1200" Height="800"
+        WindowStartupLocation="CenterScreen">
+
+    <Window.DataTemplates>
+        <DataTemplate DataType="vm:HostsViewModel">
+            <views:HostsView />
+        </DataTemplate>
+        <DataTemplate DataType="vm:InstancesViewModel">
+            <views:InstancesView />
+        </DataTemplate>
+        <DataTemplate DataType="vm:SecretsViewModel">
+            <views:SecretsView />
+        </DataTemplate>
+        <DataTemplate DataType="vm:LogsViewModel">
+            <views:LogsView />
+        </DataTemplate>
+        <DataTemplate DataType="vm:CreateInstanceViewModel">
+            <views:CreateInstanceView />
+        </DataTemplate>
+        <DataTemplate DataType="vm:SettingsViewModel">
+            <views:SettingsView />
+        </DataTemplate>
+    </Window.DataTemplates>
+
+    <DockPanel>
+        <!-- Status bar -->
+        <Border DockPanel.Dock="Bottom" Background="#1e1e2e" Padding="8,4">
+            <TextBlock Text="{Binding StatusMessage}" FontSize="12" Foreground="#a0a0a0" />
+        </Border>
+
+        <!-- Left nav -->
+        <Border DockPanel.Dock="Left" Width="180" Background="#181825" Padding="0,8">
+            <StackPanel Spacing="2">
+                <TextBlock Text="OTS Signs" FontSize="18" FontWeight="Bold" Foreground="#cdd6f4"
+                           Margin="16,8,16,16" />
+
+                <ListBox ItemsSource="{Binding NavItems}"
+                         SelectedItem="{Binding SelectedNav}"
+                         Background="Transparent"
+                         Margin="4,0">
+                    <ListBox.ItemTemplate>
+                        <DataTemplate>
+                            <TextBlock Text="{Binding}" Padding="12,8" FontSize="14" />
+                        </DataTemplate>
+                    </ListBox.ItemTemplate>
+                </ListBox>
+            </StackPanel>
+        </Border>
+
+        <!-- Main content -->
+        <Border Padding="16">
+            <ContentControl Content="{Binding CurrentView}" />
+        </Border>
+    </DockPanel>
+</Window>