refactor(ui): Icon-Faerbung zentral im ICON-PAINTING-Block

Inline Foreground/Stroke an Icons entfernt — ein lokaler Wert schlaegt jeden
Style, dadurch erreichten Hover/Checked/Disabled das Icon nicht. Farbe wird
jetzt per Klasse gewaehlt (.danger, .star-btn.on, .active), alle Zustaende
liegen in einem geordneten Block in IslandStyles.axaml.

- Path.plan-icon -> Path.icon-stroke (gilt jetzt fuer Button und ToggleButton)
- Icon.Activity als gefuellte Kontur (PathIcon fuellt, Stroke-Polyline gab Blobs)
- BloodBrightBrush als Hover-Ton fuer destruktive Icons
- icon-btn:disabled bleibt transparent statt Fluent-Grau

src/ClaudeDo.Ui/Views/Islands/Detail/TaskHeaderBar.axaml

@@ -33,10 +33,8 @@
                   IsVisible="{Binding Task.HasBranch, FallbackValue=False}">
         <!-- Icon.GitBranch is line-art: stroke-rendered, PathIcon would fill the lines away -->
         <Viewbox Width="10" Height="10">
-          <Path Data="{StaticResource Icon.GitBranch}"
-                Stroke="{DynamicResource TextDimBrush}"
-                StrokeThickness="2.4"
-                StrokeLineCap="Round" StrokeJoin="Round"/>
+          <Path Classes="icon-stroke" Data="{StaticResource Icon.GitBranch}"
+                StrokeThickness="2.4"/>
         </Viewbox>
         <TextBlock Classes="meta" Text="{Binding Task.Branch}"/>
       </StackPanel>
@@ -46,11 +44,11 @@
     <Button Grid.Column="1" Classes="icon-btn"
             Command="{Binding DeleteTaskCommand}"
             ToolTip.Tip="{loc:Tr details.deleteTaskTip}"
+            ToolTip.ShowOnDisabled="True"
             IsVisible="{Binding !IsRunning}"
             VerticalAlignment="Top"
             Margin="6,0,0,0">
-      <PathIcon Data="{StaticResource Icon.Trash}" Width="14" Height="14"
-                Foreground="{DynamicResource BloodBrush}"/>
+      <PathIcon Classes="danger" Data="{StaticResource Icon.Trash}" Width="14" Height="14"/>
     </Button>
 
     <!-- Column 1: skull button (running) -->
@@ -60,8 +58,7 @@
             IsVisible="{Binding IsRunning}"
             VerticalAlignment="Top"
             Margin="6,0,0,0">
-      <PathIcon Data="{StaticResource Icon.Skull}" Width="14" Height="14"
-                Foreground="{DynamicResource BloodBrush}"/>
+      <PathIcon Classes="danger" Data="{StaticResource Icon.Skull}" Width="14" Height="14"/>
     </Button>
 
     <!-- Column 2: gear button with agent settings flyout -->