feat(ui): Task-Zeile entdichten und Kontextmenü gruppieren (UX-Struktur A)

Gruppe 1 (Send to queue, Remove from queue, Cancel execution, Open quick
session, Refine task) ist jetzt fix sichtbar und gated per IsEnabled + Grund
statt komplett auszublenden. Planning/Schedule wandern in Untermenüs (Mark as
existierte bereits); der Planning-Kopf zeigt einen Grund, wenn er sonst leer
wäre. Refine-Button, ungesetzter Star und Dequeue-X erscheinen nur bei
Hover-oder-Selektion (TaskRowViewModel.ShowRowActions); ein gesetzter Star und
der Refining-Spinner bleiben immer sichtbar. Der Branch-Chip wandert aus der
Zeile in eine Meta-Zeile in TaskHeaderBar.

A3 headless verifiziert: Avalonia 12 zeigt ToolTips auf IsEnabled=false
Controls nur mit ToolTip.ShowOnDisabled="True" (Default ist false) — dieses
Attached Property existiert bereits und wird für die neuen Disabled-Reason-
Tooltips genutzt.

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

@@ -41,7 +41,9 @@
               Classes.dragging="{Binding IsDragging}"
               Classes.drop-target="{Binding IsDropTarget}"
               Classes.done="{Binding Done}"
-              ContextRequested="OnRowContextRequested">
+              ContextRequested="OnRowContextRequested"
+              PointerEntered="OnRowPointerEntered"
+              PointerExited="OnRowPointerExited">
         <Grid ColumnDefinitions="0,18,32,*,Auto,Auto,32" Margin="6,8,10,8">
 
         <!-- Chevron toggle (only for planning parent tasks) -->
@@ -149,12 +151,18 @@
               <TextBlock Text="{Binding CreationPhaseLabel}"/>
             </Border>
 
-            <!-- Dequeue button (visible when row is Queued, or planning parent has queued subtasks) -->
+            <!-- Dequeue button (visible when row is Queued, or planning parent has queued subtasks,
+                 AND the row is hovered or selected) -->
             <Button Classes="icon-btn dequeue-btn"
-                    IsVisible="{Binding CanRemoveFromQueue}"
                     ToolTip.Tip="{loc:Tr tasks.removeFromQueueTip}"
                     Command="{Binding $parent[ItemsControl].((vm:TasksIslandViewModel)DataContext).RemoveFromQueueCommand}"
                     CommandParameter="{Binding}">
+              <Button.IsVisible>
+                <MultiBinding Converter="{x:Static BoolConverters.And}">
+                  <Binding Path="CanRemoveFromQueue"/>
+                  <Binding Path="ShowRowActions"/>
+                </MultiBinding>
+              </Button.IsVisible>
               <PathIcon Width="10" Height="10" Data="{StaticResource Icon.X}"/>
             </Button>
 
@@ -168,16 +176,6 @@
               </StackPanel>
             </Border>
 
-            <!-- Branch chip -->
-            <Border Classes="chip chip-branch" IsVisible="{Binding HasBranch}">
-              <StackPanel Orientation="Horizontal" Spacing="4" VerticalAlignment="Center">
-                <PathIcon Width="10" Height="10"
-                          Data="{StaticResource Icon.GitBranch}"
-                          Foreground="{DynamicResource TextDimBrush}"/>
-                <TextBlock Text="{Binding Branch}"/>
-              </StackPanel>
-            </Border>
-
             <!-- Diff chip -->
             <Border Classes="chip chip-diff" IsVisible="{Binding HasDiff}">
               <StackPanel Orientation="Horizontal" Spacing="4" VerticalAlignment="Center">
@@ -203,11 +201,16 @@
         <!-- Refine button, replaced by a spinner while the refine run is in flight -->
         <Panel Grid.Column="5">
           <Button Classes="icon-btn refine-btn"
-                  IsVisible="{Binding CanRefine}"
                   VerticalAlignment="Top" Margin="0,2,0,0"
                   Command="{Binding $parent[ItemsControl].((vm:TasksIslandViewModel)DataContext).RefineTaskCommand}"
                   CommandParameter="{Binding}"
                   ToolTip.Tip="{loc:Tr tasks.refineTip}">
+            <Button.IsVisible>
+              <MultiBinding Converter="{x:Static BoolConverters.And}">
+                <Binding Path="CanRefine"/>
+                <Binding Path="ShowRowActions"/>
+              </MultiBinding>
+            </Button.IsVisible>
             <Viewbox Width="16" Height="16">
               <Path Classes="plan-icon" Data="{StaticResource Icon.Refine}"/>
             </Viewbox>
@@ -218,13 +221,19 @@
                    ToolTip.Tip="{loc:Tr tasks.refiningTip}"/>
         </Panel>
 
-        <!-- Star toggle -->
+        <!-- Star toggle: a set star always shows; unset, only on hover/selection -->
         <Button Grid.Column="6" Classes="icon-btn star-btn"
                 Classes.on="{Binding IsStarred}"
                 VerticalAlignment="Top" Margin="0,2,0,0"
                 Command="{Binding $parent[ItemsControl].((vm:TasksIslandViewModel)DataContext).ToggleStarCommand}"
                 CommandParameter="{Binding}"
                 ToolTip.Tip="{loc:Tr details.starTip}">
+          <Button.IsVisible>
+            <MultiBinding Converter="{x:Static BoolConverters.Or}">
+              <Binding Path="IsStarred"/>
+              <Binding Path="ShowRowActions"/>
+            </MultiBinding>
+          </Button.IsVisible>
           <PathIcon Width="14" Height="14" Data="{StaticResource Icon.Star}"/>
         </Button>
         </Grid>