feat(ui): Cheat-Sheet-Fenster im Hilfe-Menue

Sechs Markdown-Sheets (git, Conventional Commits, Claude CLI, Claude-Config,
dotnet CLI, PowerShell) als EmbeddedResource, gerendert im modelosen, per
Topmost anpinnbaren CheatSheetsWindow. MarkdownView bekommt dafuer das Opt-in
CommandRows: `befehl` - beschreibung wird zu Mono-Chip + Copy-Button, jede
##-Sektion landet in einem Expander. Enthaelt ausserdem: Mission Control
wird beim Oeffnen aus dem Minimiert-Zustand geholt, nicht nur aktiviert.

src/ClaudeDo.Ui/Views/WindowDialogService.cs

@@ -28,6 +28,7 @@ public sealed class WindowDialogService : IDialogService
     private readonly Window _owner;
     private MissionControlWindow? _missionControl;
     private DiffViewerView? _diffViewerWindow;
+    private CheatSheetsWindow? _cheatSheets;
 
     public WindowDialogService(Window owner) => _owner = owner;
 
@@ -182,9 +183,29 @@ public sealed class WindowDialogService : IDialogService
         _missionControl ??= new MissionControlWindow { DataContext = vm };
         if (!_missionControl.IsVisible)
             _missionControl.Show();          // modeless, independent top-level window
+        // Activate() alone does not restore a minimised window — it stays in the taskbar and the
+        // button looks dead. Un-minimise first, then take focus.
+        if (_missionControl.WindowState == WindowState.Minimized)
+            _missionControl.WindowState = WindowState.Normal;
         _missionControl.Activate();          // bring to front / focus
     }
 
+    public void ShowCheatSheets(CheatSheetsViewModel vm)
+    {
+        // Modeless and single-instance, like Mission Control: the point is to park it beside the
+        // shell, so a second window (or a modal that blocks the shell) would defeat it.
+        if (_cheatSheets is null)
+        {
+            _cheatSheets = new CheatSheetsWindow { DataContext = vm };
+            vm.CloseAction = () => _cheatSheets?.Close();
+            _cheatSheets.Closed += (_, _) => _cheatSheets = null;
+            _cheatSheets.Show(_owner);
+        }
+        if (_cheatSheets.WindowState == WindowState.Minimized)
+            _cheatSheets.WindowState = WindowState.Normal;
+        _cheatSheets.Activate();
+    }
+
     public Task<bool> ConfirmAsync(string message)
     {
         var tcs = new TaskCompletionSource<bool>();