fix(ui): reparse-check repo-scan root folder and move scan off UI thread

RepoScanner.Scan() only guarded reparse points on subdirectories found
during recursion, so a configured import root that is itself a junction
walked straight through onto other drives. Apply the same
FileAttributes.ReparsePoint check to the root before scanning.

RepoImportModalViewModel.ScanAndAdd ran the full 5-level recursive scan
synchronously on the UI thread; pointing the folder picker at a broad
directory froze the app. Offload RepoScanner.Scan to Task.Run per folder
and apply results back on the UI thread.

Add a RepoScannerTests case that creates a real junction (mklink /J) at
the scan root and asserts Scan returns empty.

src/ClaudeDo.Ui/Services/RepoScanner.cs

@@ -16,6 +16,15 @@ public static class RepoScanner
         if (string.IsNullOrWhiteSpace(parentFolder) || !Directory.Exists(parentFolder))
             return Array.Empty<RepoCandidate>();
 
+        try
+        {
+            var info = new DirectoryInfo(parentFolder);
+            if (info.Attributes.HasFlag(FileAttributes.ReparsePoint))
+                return Array.Empty<RepoCandidate>();
+        }
+        catch (Exception e) when (e is IOException or UnauthorizedAccessException)
+        { return Array.Empty<RepoCandidate>(); }
+
         var result = new List<RepoCandidate>();
         ScanDirectory(parentFolder, depth: 0, result);
         return result;

src/ClaudeDo.Ui/ViewModels/Modals/RepoImportModalViewModel.cs

@@ -75,7 +75,7 @@ public sealed partial class RepoImportModalViewModel : ViewModelBase
             ErrorReported?.Invoke(Loc.T("vm.repoImport.loadFailed", ex.Message));
         }
 
-        ScanAndAdd(_folders);
+        await ScanAndAddAsync(_folders);
         OnPropertyChanged(nameof(HasFolders));
         NotifyCreateState();
     }
@@ -88,20 +88,21 @@ public sealed partial class RepoImportModalViewModel : ViewModelBase
 
         if (added.Count == 0) return;
 
-        ScanAndAdd(added);
+        await ScanAndAddAsync(added);
         OnPropertyChanged(nameof(HasFolders));
         NotifyCreateState();
         await SaveFoldersAsync();
     }
 
-    private void ScanAndAdd(IEnumerable<string> folders)
+    private async Task ScanAndAddAsync(IEnumerable<string> folders)
     {
         var current = new HashSet<string>(
             Repos.Select(r => r.FullPath), StringComparer.OrdinalIgnoreCase);
 
         foreach (var folder in folders)
         {
-            foreach (var item in BuildCandidates(RepoScanner.Scan(folder), current, _existingDirs))
+            var found = await Task.Run(() => RepoScanner.Scan(folder));
+            foreach (var item in BuildCandidates(found, current, _existingDirs))
             {
                 item.PropertyChanged += OnItemChanged;
                 Repos.Add(item);

tests/ClaudeDo.Ui.Tests/RepoScannerTests.cs

@@ -117,6 +117,29 @@ public sealed class RepoScannerTests : IDisposable
         Assert.Empty(result);
     }
 
+    [Fact]
+    public void Scan_ReturnsEmptyWhenRootIsAReparsePoint()
+    {
+        var repo = MakeDir("real-repo");
+        Directory.CreateDirectory(Path.Combine(repo, ".git"));
+
+        var junction = Path.Combine(_root, "junction-to-real-repo");
+        var mklink = System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo
+        {
+            FileName = "cmd.exe",
+            Arguments = $"/c mklink /J \"{junction}\" \"{repo}\"",
+            UseShellExecute = false,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+        })!;
+        mklink.WaitForExit();
+        Assert.True(Directory.Exists(junction), "Failed to create test junction: " + mklink.StandardError.ReadToEnd());
+
+        var result = RepoScanner.Scan(junction);
+
+        Assert.Empty(result);
+    }
+
     [Fact]
 #pragma warning disable CA1416 // ACL manipulation is Windows-only; this test targets the Windows dev/CI environment
     public void Scan_ContinuesAfterUnreadableSubdirectory()