fix(ui): narrow RepoScanner catch to filesystem exceptions

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.Ui/Services/RepoScanner.cs

@@ -12,7 +12,8 @@ public static class RepoScanner
         var result = new List<RepoCandidate>();
         IEnumerable<string> subdirs;
         try { subdirs = Directory.EnumerateDirectories(parentFolder); }
-        catch { return Array.Empty<RepoCandidate>(); }
+        catch (Exception e) when (e is IOException or UnauthorizedAccessException)
+        { return Array.Empty<RepoCandidate>(); }
 
         foreach (var dir in subdirs)
         {