fix(ui): move ScrollViewer padding to inner content in modal bodies

Avalonia 12 excludes ScrollViewer.Padding from the scroll Extent, clipping
the last line of these five modal bodies unreachable at max scroll.

src/ClaudeDo.Ui/Views/Modals/AboutModalView.axaml

@@ -17,8 +17,8 @@
 
   <ctl:ModalShell Title="{loc:Tr modals.about.title}" CloseCommand="{Binding CloseCommand}">
     <!-- Body -->
-    <ScrollViewer Padding="20,16" HorizontalScrollBarVisibility="Disabled">
-      <Grid RowDefinitions="Auto,Auto,Auto,Auto" ColumnDefinitions="90,*,Auto" RowSpacing="10" ColumnSpacing="8">
+    <ScrollViewer HorizontalScrollBarVisibility="Disabled">
+      <Grid Margin="20,16" RowDefinitions="Auto,Auto,Auto,Auto" ColumnDefinitions="90,*,Auto" RowSpacing="10" ColumnSpacing="8">
         <TextBlock Classes="meta" Grid.Row="0" Grid.Column="0" Text="{loc:Tr modals.about.version}" VerticalAlignment="Center"/>
         <TextBlock Classes="meta" Grid.Row="0" Grid.Column="1" Text="{Binding AppVersion}" VerticalAlignment="Center"/>
         <TextBlock Classes="meta" Grid.Row="1" Grid.Column="0" Text="{loc:Tr modals.about.data}" VerticalAlignment="Center"/>

src/ClaudeDo.Ui/Views/Modals/MergeHelperSelectionModal.axaml

@@ -44,8 +44,8 @@
         <TextBlock Grid.Column="3" Classes="eyebrow" Text="{loc:Tr modals.mergeHelper.columnStatus}"/>
       </Grid>
 
-      <ScrollViewer Padding="20,2,20,8">
-        <StackPanel>
+      <ScrollViewer>
+        <StackPanel Margin="20,2,20,8">
           <TextBlock Classes="meta" Margin="0,8"
                      Text="{loc:Tr modals.mergeHelper.empty}"
                      IsVisible="{Binding !HasTasks}"/>

src/ClaudeDo.Ui/Views/Modals/MergeModalView.axaml

@@ -39,8 +39,8 @@
     </ctl:ModalShell.Footer>
 
     <!-- Body -->
-    <ScrollViewer Padding="20,16">
-      <StackPanel Spacing="12">
+    <ScrollViewer>
+      <StackPanel Margin="20,16" Spacing="12">
 
         <TextBlock Classes="title" Text="{Binding TaskTitle, StringFormat='Merging: {0}'}" />
 

src/ClaudeDo.Ui/Views/Modals/RepoImportModalView.axaml

@@ -43,8 +43,8 @@
       </StackPanel>
 
       <!-- Repo checklist -->
-      <ScrollViewer Padding="20,2,20,8">
-        <ItemsControl ItemsSource="{Binding Repos}">
+      <ScrollViewer>
+        <ItemsControl Margin="20,2,20,8" ItemsSource="{Binding Repos}">
           <ItemsControl.ItemTemplate>
             <DataTemplate DataType="vm:RepoImportItemViewModel">
               <Grid ColumnDefinitions="Auto,Auto,*,Auto" Margin="0,1"

src/ClaudeDo.Ui/Views/Modals/WorktreesOverviewModalView.axaml

@@ -134,8 +134,8 @@
       </Border>
 
       <!-- Content -->
-      <ScrollViewer Padding="20,16">
-        <StackPanel>
+      <ScrollViewer>
+        <StackPanel Margin="20,16">
           <Border IsVisible="{Binding ConflictRows.Count}"
                   Background="{DynamicResource ErrorTintBrush}"
                   BorderBrush="{DynamicResource StatusErrorBrush}"