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.

tests/ClaudeDo.Ui.Tests/ViewModels/CheatSheetsViewModelTests.cs

@@ -0,0 +1,34 @@
+using System.Linq;
+using ClaudeDo.Ui.ViewModels.Modals;
+using Xunit;
+
+namespace ClaudeDo.Ui.Tests.ViewModels;
+
+public class CheatSheetsViewModelTests
+{
+    [Fact]
+    public void LoadsEverySheetWithTitleFromHeading()
+    {
+        var vm = new CheatSheetsViewModel();
+
+        Assert.Equal(6, vm.Sheets.Count);
+        Assert.Equal(
+            ["Git", "Conventional Commits", "Claude CLI", "Claude Konfiguration", "dotnet CLI", "PowerShell"],
+            vm.Sheets.Select(s => s.Title));
+        // The heading is stripped so the window doesn't render the title twice.
+        Assert.All(vm.Sheets, s => Assert.StartsWith("## ", s.Body));
+    }
+
+    [Fact]
+    public void SelectSwitchesSheetAndIgnoresUnknownKeys()
+    {
+        var vm = new CheatSheetsViewModel();
+        Assert.Equal("git", vm.SelectedSheet!.Key);
+
+        vm.Select("dotnet-cli");
+        Assert.Equal("dotnet-cli", vm.SelectedSheet!.Key);
+
+        vm.Select("nope");
+        Assert.Equal("dotnet-cli", vm.SelectedSheet!.Key);
+    }
+}

tests/ClaudeDo.Ui.Tests/ViewModels/ListsIslandCreateListCancelTests.cs

@@ -65,6 +65,7 @@ public class ListsIslandCreateListCancelTests : IDisposable
         public Task<bool> ConfirmAsync(string message) => Task.FromResult(true);
         public Task ShowErrorAsync(string message) => Task.CompletedTask;
         public void ShowMissionControl(MissionControlViewModel vm) => throw new NotImplementedException();
+        public void ShowCheatSheets(CheatSheetsViewModel vm) => throw new NotImplementedException();
     }
 
     private sealed class ListSettingsProvider(Func<ListSettingsModalViewModel> create) : IServiceProvider

tests/ClaudeDo.Ui.Tests/ViewModels/TasksIslandMoveToListTests.cs

@@ -63,6 +63,7 @@ public class TasksIslandMoveToListTests : IDisposable
         public Task ShowLogVisualizerAsync(LogVisualizerViewModel vm) => throw new NotImplementedException();
         public Task ShowErrorAsync(string message) => Task.CompletedTask;
         public void ShowMissionControl(MissionControlViewModel vm) => throw new NotImplementedException();
+        public void ShowCheatSheets(CheatSheetsViewModel vm) => throw new NotImplementedException();
     }
 
     private TasksIslandViewModel BuildViewModel() => new(new TestDbFactory(NewContext), worker: null);

tests/ClaudeDo.Ui.Tests/Views/MarkdownCommandRowTests.cs

@@ -0,0 +1,32 @@
+using ClaudeDo.Ui.Views.Controls;
+using Xunit;
+
+namespace ClaudeDo.Ui.Tests.Views;
+
+/// <summary>
+/// Covers the command-row split only — rendering itself needs an Avalonia app, which this
+/// project has no host for.
+/// </summary>
+public class MarkdownCommandRowTests
+{
+    [Theory]
+    [InlineData("`git status -sb` — Kurzstatus mit Branch-Zeile", "git status -sb", "Kurzstatus mit Branch-Zeile")]
+    [InlineData("`git branch -d <name>` — löschen (`-D` erzwingt)", "git branch -d <name>", "löschen (`-D` erzwingt)")]
+    [InlineData("`dotnet build`", "dotnet build", "")]
+    public void SplitsCommandFromDescription(string line, string cmd, string desc)
+    {
+        Assert.True(MarkdownView.TrySplitCommand(line, out var actualCmd, out var actualDesc));
+        Assert.Equal(cmd, actualCmd);
+        Assert.Equal(desc, actualDesc);
+    }
+
+    [Theory]
+    [InlineData("Prosa ohne Befehl")]
+    [InlineData("Text mit `code` in der Mitte")]
+    [InlineData("`unclosed backtick")]
+    [InlineData("``")]
+    public void LeavesNonCommandBulletsToThePlainRenderer(string line)
+    {
+        Assert.False(MarkdownView.TrySplitCommand(line, out _, out _));
+    }
+}