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/HostsView.axaml

@@ -0,0 +1,83 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:OTSSignsOrchestrator.Desktop.ViewModels"
+             x:Class="OTSSignsOrchestrator.Desktop.Views.HostsView"
+             x:DataType="vm:HostsViewModel">
+
+    <DockPanel>
+        <!-- Toolbar -->
+        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Spacing="8" Margin="0,0,0,12">
+            <Button Content="Add Host" Command="{Binding NewHostCommand}" />
+            <Button Content="Edit" Command="{Binding EditSelectedHostCommand}" />
+            <Button Content="Test Connection" Command="{Binding TestConnectionCommand}" />
+            <Button Content="Delete" Command="{Binding DeleteHostCommand}" />
+            <Button Content="Refresh" Command="{Binding LoadHostsCommand}" />
+        </StackPanel>
+
+        <!-- Status -->
+        <TextBlock DockPanel.Dock="Bottom" Text="{Binding StatusMessage}" Margin="0,8,0,0"
+                   FontSize="12" Foreground="#a6adc8" />
+
+        <!-- Edit panel (shown when editing) -->
+        <Border DockPanel.Dock="Right" Width="350" IsVisible="{Binding IsEditing}"
+                Background="#1e1e2e" CornerRadius="8" Padding="16" Margin="12,0,0,0">
+            <ScrollViewer>
+                <StackPanel Spacing="8">
+                    <TextBlock Text="SSH Host" FontSize="16" FontWeight="SemiBold" Margin="0,0,0,8" />
+
+                    <TextBlock Text="Label" FontSize="12" />
+                    <TextBox Text="{Binding EditLabel}" Watermark="e.g. Production Swarm" />
+
+                    <TextBlock Text="Host" FontSize="12" />
+                    <TextBox Text="{Binding EditHost}" Watermark="hostname or IP" />
+
+                    <TextBlock Text="Port" FontSize="12" />
+                    <NumericUpDown Value="{Binding EditPort}" Minimum="1" Maximum="65535" />
+
+                    <TextBlock Text="Username" FontSize="12" />
+                    <TextBox Text="{Binding EditUsername}" Watermark="ssh username" />
+
+                    <CheckBox Content="Use Key Authentication" IsChecked="{Binding EditUseKeyAuth}" />
+
+                    <TextBlock Text="Private Key Path" FontSize="12"
+                               IsVisible="{Binding EditUseKeyAuth}" />
+                    <TextBox Text="{Binding EditPrivateKeyPath}" Watermark="~/.ssh/id_rsa"
+                             IsVisible="{Binding EditUseKeyAuth}" />
+
+                    <TextBlock Text="Key Passphrase (optional)" FontSize="12"
+                               IsVisible="{Binding EditUseKeyAuth}" />
+                    <TextBox Text="{Binding EditKeyPassphrase}" PasswordChar="●"
+                             IsVisible="{Binding EditUseKeyAuth}" />
+
+                    <TextBlock Text="Password (if not using key)" FontSize="12"
+                               IsVisible="{Binding !EditUseKeyAuth}" />
+                    <TextBox Text="{Binding EditPassword}" PasswordChar="●"
+                             IsVisible="{Binding !EditUseKeyAuth}" />
+
+                    <StackPanel Orientation="Horizontal" Spacing="8" Margin="0,12,0,0">
+                        <Button Content="Save" Command="{Binding SaveHostCommand}" />
+                        <Button Content="Cancel" Command="{Binding CancelEditCommand}" />
+                    </StackPanel>
+                </StackPanel>
+            </ScrollViewer>
+        </Border>
+
+        <!-- Host list -->
+        <DataGrid ItemsSource="{Binding Hosts}"
+                  SelectedItem="{Binding SelectedHost}"
+                  AutoGenerateColumns="False"
+                  IsReadOnly="True"
+                  GridLinesVisibility="Horizontal"
+                  CanUserResizeColumns="True">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Label" Binding="{Binding Label}" Width="150" />
+                <DataGridTextColumn Header="Host" Binding="{Binding Host}" Width="200" />
+                <DataGridTextColumn Header="Port" Binding="{Binding Port}" Width="60" />
+                <DataGridTextColumn Header="User" Binding="{Binding Username}" Width="100" />
+                <DataGridCheckBoxColumn Header="Key Auth" Binding="{Binding UseKeyAuth}" Width="70" />
+                <DataGridTextColumn Header="Last Tested" Binding="{Binding LastTestedAt, StringFormat='{}{0:g}'}" Width="150" />
+                <DataGridCheckBoxColumn Header="OK" Binding="{Binding LastTestSuccess}" Width="50" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>