Merge branch 'v0.3.1-theming' into v0.4-opcua

MachineConfigView was two left-pinned cards (MaxWidth 480/640, HAlign Left)
stacked in a DockPanel — right half of wide window empty, items list capped at
320px. Now root Grid Auto,*,Auto: header top, footer (validation + Save/Cancel)
bottom full-width, body Grid Auto,* — fixed 380px form left, data-items card
stretches to fill width + height (scrollable). Layout only; no binding/VM/command
change. Dashboard/Detail already fill correctly — untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Junction.App/Views/MachineConfigView.axaml

@@ -8,29 +8,19 @@
              x:DataType="vm:MachineConfigViewModel"
              x:CompileBindings="True">
 
-  <DockPanel Margin="20">
+  <!-- header / body / footer -->
+  <Grid Margin="20" RowDefinitions="Auto,*,Auto">
 
     <!-- Header -->
-    <TextBlock DockPanel.Dock="Top" Classes="h1"
+    <TextBlock Grid.Row="0" Classes="h1"
                Text="{Binding Title}"
                Margin="0,0,0,16" />
 
-    <!-- Action bar -->
-    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal" Spacing="12" Margin="0,16,0,0">
-      <Button Classes="accent" Content="Save" Command="{Binding SaveCommand}" IsDefault="True" />
-      <Button Content="Cancel" Command="{Binding CancelCommand}" />
-    </StackPanel>
-
-    <!-- Inline validation hint -->
-    <TextBlock DockPanel.Dock="Bottom"
-               Text="{Binding ValidationError}"
-               IsVisible="{Binding HasValidationError}"
-               Foreground="{DynamicResource DangerBrush}"
-               TextWrapping="Wrap"
-               Margin="0,12,0,0" />
+    <!-- Body: fixed form column + stretching data-items column -->
+    <Grid Grid.Row="1" ColumnDefinitions="Auto,*">
 
       <!-- Form -->
-    <Border DockPanel.Dock="Top" Classes="card" MaxWidth="480" HorizontalAlignment="Left">
+      <Border Grid.Column="0" Classes="card" Width="380" VerticalAlignment="Top">
         <StackPanel Spacing="12">
 
           <StackPanel Spacing="4">
@@ -59,8 +49,8 @@
         </StackPanel>
       </Border>
 
-    <!-- Data items to monitor (fills remaining space) -->
-    <Border Classes="card" Margin="0,16,0,0" MaxWidth="640" HorizontalAlignment="Left">
+      <!-- Data items to monitor (fills remaining width + height) -->
+      <Border Grid.Column="1" Classes="card" Margin="16,0,0,0" HorizontalAlignment="Stretch">
         <DockPanel>
 
           <TextBlock DockPanel.Dock="Top" Classes="h2" Text="Data items to monitor"
@@ -99,8 +89,8 @@
             </Grid>
           </Border>
 
-        <!-- Scrollable checklist -->
-        <ScrollViewer MaxHeight="320">
+          <!-- Scrollable checklist (fills remaining height) -->
+          <ScrollViewer>
             <ItemsControl ItemsSource="{Binding AvailableItems}">
               <ItemsControl.ItemTemplate>
                 <DataTemplate x:DataType="vm:SelectableDataItemViewModel">
@@ -123,5 +113,23 @@
 
         </DockPanel>
       </Border>
-  </DockPanel>
+    </Grid>
+
+    <!-- Footer: validation hint + action bar, full width -->
+    <StackPanel Grid.Row="2" Spacing="0">
+      <!-- Inline validation hint -->
+      <TextBlock Text="{Binding ValidationError}"
+                 IsVisible="{Binding HasValidationError}"
+                 Foreground="{DynamicResource DangerBrush}"
+                 TextWrapping="Wrap"
+                 Margin="0,12,0,0" />
+
+      <!-- Action bar -->
+      <StackPanel Orientation="Horizontal" Spacing="12" Margin="0,16,0,0">
+        <Button Classes="accent" Content="Save" Command="{Binding SaveCommand}" IsDefault="True" />
+        <Button Content="Cancel" Command="{Binding CancelCommand}" />
+      </StackPanel>
+    </StackPanel>
+
+  </Grid>
 </UserControl>