feat(ui): show mergeability and surface approve conflicts in the work console

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -0,0 +1,62 @@
+using ClaudeDo.Ui.Services;
+using ClaudeDo.Ui.ViewModels.Islands;
+
+namespace ClaudeDo.Ui.Tests.ViewModels;
+
+public class MergePreviewPresenterTests
+{
+    [Fact]
+    public void Clean_Plural()
+    {
+        var (text, clean, conflict) = MergePreviewPresenter.Describe(
+            new MergePreviewDto("clean", System.Array.Empty<string>(), 3));
+        Assert.Equal("Merges cleanly · 3 files", text);
+        Assert.True(clean);
+        Assert.False(conflict);
+    }
+
+    [Fact]
+    public void Clean_Singular()
+    {
+        var (text, _, _) = MergePreviewPresenter.Describe(
+            new MergePreviewDto("clean", System.Array.Empty<string>(), 1));
+        Assert.Equal("Merges cleanly · 1 file", text);
+    }
+
+    [Fact]
+    public void Conflict_ListsUpToThree()
+    {
+        var (text, clean, conflict) = MergePreviewPresenter.Describe(
+            new MergePreviewDto("conflict", new[] { "a.cs", "b.cs" }, 0));
+        Assert.Equal("Conflicts in a.cs, b.cs", text);
+        Assert.False(clean);
+        Assert.True(conflict);
+    }
+
+    [Fact]
+    public void Conflict_TruncatesWithMore()
+    {
+        var (text, _, _) = MergePreviewPresenter.Describe(
+            new MergePreviewDto("conflict", new[] { "a", "b", "c", "d", "e" }, 0));
+        Assert.Equal("Conflicts in a, b, c (+2 more)", text);
+    }
+
+    [Fact]
+    public void Unavailable_IsMuted()
+    {
+        var (text, clean, conflict) = MergePreviewPresenter.Describe(
+            new MergePreviewDto("unavailable", System.Array.Empty<string>(), 0));
+        Assert.Equal("Mergeability unknown", text);
+        Assert.False(clean);
+        Assert.False(conflict);
+    }
+
+    [Fact]
+    public void Null_IsEmpty()
+    {
+        var (text, clean, conflict) = MergePreviewPresenter.Describe(null);
+        Assert.Equal("", text);
+        Assert.False(clean);
+        Assert.False(conflict);
+    }
+}