fix(merge): unresolved conflicts compose to empty, not Ours (+ review nits)

Code-review follow-ups before push:
- MergeFile.ResultText/Compose() fell back to Ours for unresolved conflicts while
  the editor seeds them empty — align both on empty so the public model matches the
  pane and Continue can't silently auto-accept Ours.
- Bound the gutter re-layout retry (was an unbounded Background re-post when the
  editor isn't laid out, e.g. minimized).
- Pluralize the readout ('1 conflict' not '1 conflicts'). Tests updated. Ui 128 green.

src/ClaudeDo.Ui/ViewModels/Conflicts/ConflictResolverViewModel.cs

@@ -81,7 +81,7 @@ public sealed partial class ConflictResolverViewModel : ObservableObject
             if (ActiveFile is null || ActiveFile.Conflicts.Count == 0) return "No text conflicts";
             var count = ActiveFile.Conflicts.Count;
             var resolved = ActiveFile.Conflicts.Count(c => c.IsResolved);
-            return $"{count} conflicts · {resolved} resolved";
+            return $"{count} {(count == 1 ? "conflict" : "conflicts")} · {resolved} resolved";
         }
     }