fix: update loading state handling in CalendarPage and DutyList components

- Set isLoading to false in CalendarPage to prevent unnecessary loading indicators.
- Removed the loading spinner from CalendarHeader and adjusted rendering logic in DutyList to show a placeholder when data is not yet loaded for the month.
- Enhanced tests in DutyList to verify behavior when data is empty and when data is loading, ensuring accurate user feedback during data fetching.

webapp-next/src/components/duty/DutyList.test.tsx

@@ -35,17 +35,27 @@ describe("DutyList", () => {
     useAppStore.getState().setCurrentMonth(new Date(2025, 1, 1)); // Feb 2025
   });
 
-  it("renders no duties message when duties empty", () => {
+  it("renders no duties message when duties empty and data loaded for month", () => {
     useAppStore.getState().setDuties([]);
+    useAppStore.getState().batchUpdate({ dataForMonthKey: "2025-02" });
     render(<DutyList />);
     expect(screen.getByText(/No duties this month/i)).toBeInTheDocument();
   });
 
+  it("renders quiet placeholder when data not yet loaded for month", () => {
+    useAppStore.getState().setDuties([]);
+    useAppStore.getState().batchUpdate({ dataForMonthKey: null });
+    render(<DutyList />);
+    expect(screen.queryByText(/No duties this month/i)).not.toBeInTheDocument();
+    expect(document.querySelector('[aria-busy="true"]')).toBeInTheDocument();
+  });
+
   it("renders duty with full_name and time range", () => {
     useAppStore.getState().setDuties([
       duty("Иванов", "2025-02-25T09:00:00Z", "2025-02-25T18:00:00Z"),
     ]);
     useAppStore.getState().setCurrentMonth(new Date(2025, 1, 1));
+    useAppStore.getState().batchUpdate({ dataForMonthKey: "2025-02" });
     render(<DutyList />);
     expect(screen.getByText("Иванов")).toBeInTheDocument();
   });
@@ -58,6 +68,7 @@ describe("DutyList", () => {
       }),
     ]);
     useAppStore.getState().setCurrentMonth(new Date(2025, 2, 1));
+    useAppStore.getState().batchUpdate({ dataForMonthKey: "2025-03" });
     render(<DutyList />);
     expect(screen.getAllByText("Alice").length).toBeGreaterThanOrEqual(1);
     expect(document.querySelector('a[href^="tel:"]')).toBeInTheDocument();