feat(ui): add RepoImportModalViewModel with candidate merge logic

tests/ClaudeDo.Ui.Tests/RepoImportCandidatesTests.cs

@@ -0,0 +1,48 @@
+using ClaudeDo.Ui.Services;
+using ClaudeDo.Ui.ViewModels.Modals;
+
+namespace ClaudeDo.Ui.Tests;
+
+public sealed class RepoImportCandidatesTests
+{
+    [Fact]
+    public void BuildCandidates_NewRepo_IsCheckedAndNotAlreadyAdded()
+    {
+        var found = new[] { new RepoCandidate("repo-a", @"C:\src\repo-a") };
+        var current = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        var existing = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        var items = RepoImportModalViewModel.BuildCandidates(found, current, existing);
+
+        Assert.Single(items);
+        Assert.True(items[0].IsChecked);
+        Assert.False(items[0].AlreadyAdded);
+        Assert.Equal("repo-a", items[0].Name);
+    }
+
+    [Fact]
+    public void BuildCandidates_ExistingWorkingDir_IsMarkedAlreadyAdded()
+    {
+        var found = new[] { new RepoCandidate("repo-a", @"C:\src\repo-a") };
+        var current = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        var existing = new HashSet<string>(new[] { @"c:\src\repo-a" }, StringComparer.OrdinalIgnoreCase);
+
+        var items = RepoImportModalViewModel.BuildCandidates(found, current, existing);
+
+        Assert.Single(items);
+        Assert.True(items[0].AlreadyAdded);
+        Assert.True(items[0].IsChecked); // already-added rows render ticked
+    }
+
+    [Fact]
+    public void BuildCandidates_SkipsPathsAlreadyShown()
+    {
+        var found = new[] { new RepoCandidate("repo-a", @"C:\src\repo-a") };
+        var current = new HashSet<string>(new[] { @"c:\src\repo-a" }, StringComparer.OrdinalIgnoreCase);
+        var existing = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+        var items = RepoImportModalViewModel.BuildCandidates(found, current, existing);
+
+        Assert.Empty(items);
+    }
+}