feat(ui): wählbares Listen-Icon und aufgeräumter Task-Detail-Header

Listen bekommen eine Icon-Spalte (Migration AddListIcon) und einen Icon-Picker
in den Listeneinstellungen; 34 kuratierte Geometrien aus der Icon-Bibliothek,
Fallback auf "Folder" bei unbekanntem Key.

Der Metadata-Footer im Task-Detail entfällt; created-at wandert in die
Header-Zeile neben das ID-Badge, der Close-Button (und CloseDetailsCommand)
fällt weg.

src/ClaudeDo.Ui/Views/Modals/ListSettingsModalView.axaml

@@ -39,6 +39,7 @@
                Background="Transparent" Margin="12,16,8,8"
                VerticalAlignment="Top">
         <ListBoxItem Content="{loc:Tr modals.listSettings.sectionGeneral}"/>
+        <ListBoxItem Content="{loc:Tr modals.listSettings.sectionIcon}"/>
         <ListBoxItem Content="{loc:Tr modals.listSettings.sectionAgent}"/>
         <ListBoxItem Content="{loc:Tr modals.listSettings.sectionVerify}"/>
       </ListBox>
@@ -113,6 +114,35 @@
           </ScrollViewer>
         </TabItem>
 
+        <!-- ICON -->
+        <TabItem Header="{loc:Tr modals.listSettings.sectionIcon}">
+          <ScrollViewer>
+            <StackPanel Spacing="8" Margin="0,8,0,0">
+              <TextBlock Classes="field-label" Text="{loc:Tr modals.listSettings.icon}"/>
+              <ListBox ItemsSource="{Binding Icons}"
+                       SelectedItem="{Binding Icon, Mode=TwoWay}"
+                       Background="Transparent" BorderThickness="0"
+                       HorizontalAlignment="Left">
+                <ListBox.ItemsPanel>
+                  <ItemsPanelTemplate>
+                    <WrapPanel/>
+                  </ItemsPanelTemplate>
+                </ListBox.ItemsPanel>
+                <ListBox.ItemTemplate>
+                  <DataTemplate x:DataType="x:String">
+                    <!-- No Foreground here on purpose: the icon inherits the container's, so the
+                         selected/hover states of ListBoxItem reach it (see Ui/CLAUDE.md). -->
+                    <PathIcon Width="20" Height="20" Margin="6"
+                              Data="{Binding Converter={StaticResource IconKey}}"/>
+                  </DataTemplate>
+                </ListBox.ItemTemplate>
+              </ListBox>
+              <TextBlock Text="{loc:Tr modals.listSettings.iconHint}"
+                         Opacity="0.6" FontSize="12" TextWrapping="Wrap"/>
+            </StackPanel>
+          </ScrollViewer>
+        </TabItem>
+
         <!-- AGENT -->
         <TabItem Header="{loc:Tr modals.listSettings.sectionAgent}">
           <ScrollViewer>