feat(ui): My Day actions, orphan-aware grouping, menu restructure

Pending UI work:
- My Day add/remove context actions on task rows (parent removal cascades to children)
- orphan-aware grouping: a child whose parent isn't in view renders as a top-level row, not an indented draft
- shell menu restructure (Worker / Repositories submenus); 'Finalize plan' action, drop 'Queue subtasks sequentially'
- notes editor refinements
- subtask-row hover tweak (Surface3, no transition)
- bump Avalonia 12.0.0 -> 12.0.4

src/ClaudeDo.Ui/Design/IslandStyles.axaml

@@ -871,14 +871,9 @@
     <Setter Property="Padding"      Value="8,5" />
     <Setter Property="CornerRadius" Value="6" />
     <Setter Property="Background"   Value="Transparent" />
-    <Setter Property="Transitions">
-      <Transitions>
-        <BrushTransition Property="Background" Duration="0:0:0.10"/>
-      </Transitions>
-    </Setter>
   </Style>
   <Style Selector="Border.subtask-row:pointerover">
-    <Setter Property="Background" Value="{StaticResource Surface2Brush}" />
+    <Setter Property="Background" Value="{StaticResource Surface3Brush}" />
   </Style>
   <Style Selector="Border.subtask-row.done TextBlock.subtask-title">
     <Setter Property="Opacity"         Value="0.5" />