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/Islands/ListsIslandView.axaml

@@ -103,7 +103,6 @@
                   <PathIcon Grid.Column="0" Classes="list-icon"
                             Width="14" Height="14"
                             Data="{Binding IconKey, Converter={StaticResource IconKey}}"
-                            Foreground="{DynamicResource TextMuteBrush}"
                             HorizontalAlignment="Center" VerticalAlignment="Center"/>
                   <!-- Name -->
                   <TextBlock Grid.Column="1" Classes="list-label"
@@ -177,11 +176,11 @@
                             HorizontalAlignment="Left" VerticalAlignment="Center"
                             Margin="-8,0,0,0"/>
                   </Border>
-                  <!-- Color dot (6px circle, color from DotColorKey) -->
-                  <Ellipse Grid.Column="0"
-                           Width="6" Height="6"
-                           Fill="{Binding DotColorKey, Converter={StaticResource DotBrush}}"
-                           HorizontalAlignment="Center" VerticalAlignment="Center"/>
+                  <!-- Icon (list-settings → Icon tab; "Folder" when unset) -->
+                  <PathIcon Grid.Column="0" Classes="list-icon"
+                            Width="14" Height="14"
+                            Data="{Binding IconKey, Converter={StaticResource IconKey}}"
+                            HorizontalAlignment="Center" VerticalAlignment="Center"/>
                   <!-- Name -->
                   <TextBlock Grid.Column="1" Classes="list-label"
                              Text="{Binding Name}"