Melhorias no layout e usabilidade de MainWindow

- Associado o evento de carregamento da janela ao método `Window_Loaded` em MainWindow.xaml.
- Ajustada a estrutura de `<Grid.RowDefinitions>` para melhorar o layout.
- Adicionado `<TextBox>` `txtEmpresaSearch` vinculado ao ViewModel para busca de empresas.
- Definida altura fixa de `213` no `<ListView>` para consistência visual.
- Implementado o método `Window_Loaded` em MainWindow.xaml.cs para definir foco inicial no campo de busca.

MainWindow.xaml

@@ -5,13 +5,14 @@
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:local="clr-namespace:BD_empresa"
         mc:Ignorable="d"
+        Loaded="Window_Loaded"
         Title="Pesquisar Unidades" Height="650" Width="800">
     <Grid>
 
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto" />
             <RowDefinition Height="Auto" />
-            <RowDefinition Height="*" />
+            <RowDefinition Height="Auto" />
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
         <Grid.ColumnDefinitions>
@@ -38,6 +39,7 @@
                     Command="{Binding RefreshCommand}"
                     VerticalAlignment="Center" />
             <TextBox 
+                     x:Name="txtEmpresaSearch" 
                      Margin="0,0,10,0"
                      VerticalAlignment="Center"
                      Grid.Column="2"
@@ -54,7 +56,7 @@
                 <RowDefinition Height="*" />
             </Grid.RowDefinitions>
             <TextBlock Text="Empresas:" Margin="10,0,10,0" FontWeight="Bold" Grid.Row="0"/>
-            <ListView ItemsSource="{Binding Clientes}" Margin="10" SelectedItem="{Binding SelectedCliente, Mode=TwoWay}" Grid.Row="1">
+            <ListView ItemsSource="{Binding Clientes}" Height="213" Margin="10" SelectedItem="{Binding SelectedCliente, Mode=TwoWay}" Grid.Row="1">
                 <ListView.View>
                     <GridView>
                         <GridViewColumn Header="Gestão" DisplayMemberBinding="{Binding Gestao}" Width="70" />

MainWindow.xaml.cs

@@ -24,6 +24,10 @@ namespace BD_empresa
             var accessService = new Data.AccessService($"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={accessDbPath};Jet OLEDB:Database Password=gds21");
             DataContext = new ViewModels.MainWindowViewModel(accessService);
         }
+        private void Window_Loaded(object sender, RoutedEventArgs e)
+        {
+            txtEmpresaSearch.Focus();
+        }
 
         private void UnidadeListView_MouseDoubleClick(object sender, System.Windows.Input.MouseButtonEventArgs e)
         {