test: fix obsolete create_task kind=plan passthrough test

test_create_task_passes_kind asserted create_task forwards kind=plan; the
hard-retire guard now rejects that. Exercise passthrough with kind=issue
instead. (Service-level create_note still accepts task_kind=plan by design —
the guard lives at the user-facing tool/route layer, not the primitive.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_mcp_tool_tasks_kind.py

@@ -20,11 +20,12 @@ def _fake_note(task_kind="work"):
 
 @pytest.mark.asyncio
 async def test_create_task_passes_kind():
-    mock = AsyncMock(return_value=_fake_note(task_kind="plan"))
+    # kind=plan is retired (plans are milestones); 'issue' exercises passthrough.
+    mock = AsyncMock(return_value=_fake_note(task_kind="issue"))
     with patch("scribe.mcp.tools.tasks.notes_svc.create_note", mock):
         from scribe.mcp.tools.tasks import create_task
-        await create_task(title="P", kind="plan")
-    assert mock.call_args.kwargs["task_kind"] == "plan"
+        await create_task(title="P", kind="issue")
+    assert mock.call_args.kwargs["task_kind"] == "issue"
 
 
 @pytest.mark.asyncio