fix(prompts): only ask list-handler dedupe questions when a candidate exists

Phase 1 previously asked the user to confirm the absence of duplicates
even when no candidate pair was found. The handler now decides that
itself and moves straight to Phase 2; per-pair questions remain when
at least one candidate exists.

tests/ClaudeDo.Data.Tests/PromptFilesTests.cs

@@ -77,6 +77,16 @@ public class PromptFilesTests
         Assert.DoesNotContain("run_task_now(", d);  // single override slot — must not batch-start
     }
 
+    [Fact]
+    public void DefaultFor_merge_helper_only_asks_dedupe_questions_when_a_candidate_exists()
+    {
+        var d = PromptFiles.DefaultFor(PromptKind.MergeHelper);
+        Assert.Contains("move straight to Phase 2", d);
+        Assert.Contains("do not ask the user to confirm the absence of duplicates", d);
+        Assert.Contains("Cancel nothing without an explicit answer", d);
+        Assert.DoesNotContain("whenever you are unsure", d);
+    }
+
     [Fact]
     public void DefaultFor_merge_helper_initial_has_repo_token()
     {