feat(ui): Erststart-Banner und Textkette Repo→Task→Queue→Review (UX-Struktur C)

HasNoLinkedRepo on ListsIslandViewModel drives a dismiss-less banner under the
Lists-Island header when no User list has a linked repo; recomputed on load
and after list CRUD / list-settings save. Sharpens the #192 empty-state texts
into one readable chain (banner → no-repo list → repo-linked list) and adds a
line to the WorkConsole review gate spelling out that Approve also merges the
whole unit.

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

@@ -30,6 +30,24 @@
       </StackPanel>
     </Border>
 
+    <!-- ── No-repo banner — visible until any User list has a linked working dir; no
+         dismiss, no persisted state, comes back if the last repo link is removed. ── -->
+    <Border DockPanel.Dock="Top"
+            IsVisible="{Binding HasNoLinkedRepo}"
+            Margin="12,0,12,12"
+            Background="{DynamicResource DeepBrush}"
+            BorderBrush="{DynamicResource LineBrush}"
+            BorderThickness="1"
+            CornerRadius="6"
+            Padding="14,10">
+      <StackPanel Spacing="8">
+        <TextBlock Classes="body" Text="{loc:Tr lists.noRepoBannerText}" TextWrapping="Wrap"/>
+        <Button Classes="btn" HorizontalAlignment="Right"
+                Content="{loc:Tr lists.noRepoBannerButton}"
+                Command="{Binding OpenRepoImportCommand}"/>
+      </StackPanel>
+    </Border>
+
     <!-- ── Footer ── -->
     <Border DockPanel.Dock="Bottom"
             BorderBrush="{DynamicResource LineBrush}" BorderThickness="0,1,0,0"