fix(ui): keep task rows without a chain relation flat

The indent column was hardcoded to 24px, so every row reserved the
gutter even with no child/chain relation. Restore Auto sizing with the
width back on the Border, which collapses to 0 while it is invisible.
Move the step badge into column 1 with a negative margin so its desired
width can never widen the Auto column (same on-screen position).

src/ClaudeDo.Ui/Views/Islands/TaskRowView.axaml

@@ -19,10 +19,11 @@
     </Grid>
 
     <!-- Indent wrapper: col 0 = 24px child/chain indent track, col 1 = content -->
-    <Grid Grid.Row="1" ColumnDefinitions="24,*">
+    <Grid Grid.Row="1" ColumnDefinitions="Auto,*">
 
-      <!-- Indent track (only while the parent/chain-head shares this view; orphaned rows render flat) -->
-      <Border Grid.Column="0" VerticalAlignment="Stretch">
+      <!-- Indent track (only while the parent/chain-head shares this view; orphaned rows render flat).
+           Auto + Width: collapses to 0 on rows with no chain/child relation, so those stay flat. -->
+      <Border Grid.Column="0" Width="24" VerticalAlignment="Stretch">
         <Border.IsVisible>
           <MultiBinding Converter="{x:Static BoolConverters.Or}">
             <Binding Path="ShowAsChild"/>
@@ -33,11 +34,12 @@
                    HorizontalAlignment="Right" Margin="0,4"/>
       </Border>
 
-      <!-- Chain step badge: centered on the rail line, half laid over the card's left edge -->
-      <Border Grid.Column="0" Grid.ColumnSpan="2" Classes="chain-step-badge"
+      <!-- Chain step badge: centered on the rail line, half laid over the card's left edge.
+           Lives in col 1 with a negative margin so it never widens the Auto indent column. -->
+      <Border Grid.Column="1" Classes="chain-step-badge"
               IsVisible="{Binding ShowAsChainMember}"
               HorizontalAlignment="Left" VerticalAlignment="Center"
-              Margin="16,0,0,0">
+              Margin="-8,0,0,0">
         <TextBlock Text="{Binding ChainStep}"/>
       </Border>