feat(mcp): add legacy workstream alias deprecation warnings (STATE-WP-0069 T03)

Legacy MCP tools and the workstreams resource now return _deprecation payloads
pointing to workplan-named replacements. get_domain_summary uses workplan-first
prose and exposes a workplans key alongside the legacy workstreams field.

tests/test_mcp_write_tools.py

@@ -75,8 +75,24 @@ class TestMCPWriteTools:
         )
 
         assert body["id"] == "wp-1"
+        assert body["_deprecation"]["replacement"] == "create_workplan"
         assert [path for path, _ in calls] == ["/workplans", "/progress"]
 
+    async def test_list_workstreams_legacy_alias_wraps_deprecation(self, monkeypatch):
+        monkeypatch.setattr(
+            server,
+            "_get",
+            lambda path, params=None: [{"id": "wp-1", "title": "Example"}]
+            if path == "/workplans"
+            else [],
+        )
+
+        body = await _call_tool("list_workstreams", {})
+
+        assert body["_deprecation"]["replacement"] == "list_workplans"
+        assert body["workplans"] == [{"id": "wp-1", "title": "Example"}]
+        assert body["workstreams"] == body["workplans"]
+
     async def test_create_task_returns_rest_shape_and_emits_progress(self, monkeypatch):
         calls: list[tuple[str, dict[str, Any]]] = []