feat: deliver schema 15 monthly settlement lifecycle

tests/test_dashboard_menu_transition.py

@@ -43,6 +43,18 @@ def test_sidebar_selection_updates_only_page_query_parameter(monkeypatch):
     assert query == {"page": "거래내역", "month": "2026-06", "account_id": "checking"}
 
 
+def test_sidebar_monthly_settlement_serializes_canonical_page(monkeypatch):
+    query = {"page": "요약", "month": "2026-06"}
+    state = {"dashboard_page": "월정산"}
+    callback = {}
+    monkeypatch.setattr(common.st, "query_params", query)
+    monkeypatch.setattr(common.st, "session_state", state)
+    monkeypatch.setattr(common.st, "radio", lambda *args, **kwargs: callback.setdefault("fn", kwargs["on_change"]) or state["dashboard_page"])
+    common.render_sidebar_nav(PAGES, "월정산")
+    callback["fn"]()
+    assert query == {"page": "monthly_settlement", "month": "2026-06"}
+
+
 def test_missing_or_unknown_page_falls_back_to_overview():
     assert common.validate_dashboard_page(None, PAGES) == "요약"
     assert common.validate_dashboard_page("not-a-page", PAGES) == "요약"