feat(ui): add OperationStatus feedback primitive and OperationIndicator control

Foundation for long-running-operation feedback (P0-1). OperationStatus tracks
IsRunning/ShowIndicator(300ms grace)/Elapsed/IsStalled(60s since last Report)
via an injectable TimeProvider, no static timer. OperationIndicator binds a
status to the shared spinner style. Pre-provisions ops.* locale keys for
groups A and C; no ViewModel wired up yet.

src/ClaudeDo.Ui/Views/Controls/OperationIndicator.axaml

@@ -0,0 +1,16 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:svc="using:ClaudeDo.Ui.Services"
+             xmlns:loc="using:ClaudeDo.Ui.Localization"
+             x:Class="ClaudeDo.Ui.Views.Controls.OperationIndicator"
+             x:DataType="svc:OperationStatus">
+  <StackPanel Orientation="Horizontal" Spacing="{StaticResource SpaceSm}" VerticalAlignment="Center"
+              IsVisible="{Binding ShowIndicator}">
+    <Ellipse Classes="spinner" VerticalAlignment="Center"/>
+    <TextBlock Classes="meta" VerticalAlignment="Center" Text="{Binding Label}"/>
+    <TextBlock Classes="meta" VerticalAlignment="Center" Text="{Binding Elapsed}"/>
+    <TextBlock Classes="meta" VerticalAlignment="Center" Opacity="0.7"
+               Text="{loc:Tr ops.stalledHint}"
+               IsVisible="{Binding IsStalled}"/>
+  </StackPanel>
+</UserControl>