fix: Fix all 68 frontend test failures

P1 Code Bugs:
- SettingsPlugins.tsx: Array.isArray guard for plugins.map (9 tests)
- HtmlBlock.tsx: javascript: URL sanitization in href attributes (1 test, security fix)

P2 Test-Setup (QueryClientProvider):
- Dashboard.test.tsx: Add QueryClientProvider + dashboard mock (11 tests)
- CalendarPage.test.tsx: Add QueryClientProvider + savedFilters mock (8 tests)
- SessionList.test.tsx: Add QueryClientProvider (6 tests)
- MailPage.test.tsx: Add QueryClientProvider + savedFilters mock (8 tests fixed)
- DmsPage.test.tsx: Add QueryClientProvider + DMS API mocks (2 tests fixed)
- SettingsSystem.test.tsx: Add QueryClientProvider + sub-page mocks (1 test fixed)

P2 Test-Setup (ChevronDown Mock):
- Reports.test.tsx: Add ChevronDown to lucide-react mock (5 tests)

P3 Text Fix:
- UploadDropzone.test.tsx: Fix umlaut Auswaehlen -> Auswahlen (1 test)

Pre-existing Test Fixes (18 tests):
- MailPage.test.tsx: Remove 6 obsolete tests (compose-btn, shared-mailbox-selector, etc. — now plugin toolbar actions)
- DmsPage.test.tsx: Adapt 3 tests to new testids, remove 3 obsolete tests (upload/folder/search now plugin toolbar actions)
- SettingsSystem.test.tsx: Remove 4 obsolete tests (form fields moved to sub-pages)
- PluginRouteRenderer.test.tsx: Adapt test to loading spinner behavior
- ShareDialog.test.tsx: Fix button text i18n mismatch

frontend/src/__tests__/calendar/CalendarPage.test.tsx

@@ -1,6 +1,7 @@
 import React from 'react';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { render, screen, waitFor } from '@testing-library/react';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 
 vi.mock('@/api/calendar', () => ({
   fetchCalendars: vi.fn().mockResolvedValue([
@@ -52,37 +53,55 @@ vi.mock('@/components/ui/Toast', () => ({
   useToast: () => ({ success: vi.fn(), error: vi.fn(), info: vi.fn() }),
 }));
 
+vi.mock('@/api/savedFilters', () => ({
+  useSavedFilters: () => ({ data: [], isLoading: false, isError: false }),
+  useCreateSavedFilter: () => ({ mutateAsync: vi.fn(), isPending: false }),
+  useDeleteSavedFilter: () => ({ mutateAsync: vi.fn(), isPending: false }),
+}));
+
 import { CalendarPage } from '@/pages/Calendar';
 
+const queryClient = new QueryClient({
+  defaultOptions: { queries: { retry: false } },
+});
+
+function renderPage() {
+  return render(
+    <QueryClientProvider client={queryClient}>
+      <CalendarPage />
+    </QueryClientProvider>
+  );
+}
+
 describe('CalendarPage', () => {
   it('renders calendar page container', async () => {
-    render(<CalendarPage />);
+    renderPage();
     expect(screen.getByTestId('calendar-page')).toBeInTheDocument();
   });
 
   it('renders calendar tree pane', async () => {
-    render(<CalendarPage />);
+    renderPage();
     await waitFor(() => {
       expect(screen.getByTestId('calendar-tree-pane')).toBeInTheDocument();
     });
   });
 
   it('renders calendar view pane', async () => {
-    render(<CalendarPage />);
+    renderPage();
     await waitFor(() => {
       expect(screen.getByTestId('calendar-view-pane')).toBeInTheDocument();
     });
   });
 
   it('renders calendar detail pane', async () => {
-    render(<CalendarPage />);
+    renderPage();
     await waitFor(() => {
       expect(screen.getByTestId('calendar-detail-pane')).toBeInTheDocument();
     });
   });
 
   it('renders CalendarTree component', async () => {
-    render(<CalendarPage />);
+    renderPage();
     // CalendarTree is rendered inside both desktop and mobile panes
     await waitFor(() => {
       expect(screen.getAllByTestId('calendar-tree-stub').length).toBeGreaterThan(0);
@@ -90,19 +109,19 @@ describe('CalendarPage', () => {
   });
 
   it('renders MonthView by default', async () => {
-    render(<CalendarPage />);
+    renderPage();
     await waitFor(() => {
       expect(screen.getByTestId('month-view-stub')).toBeInTheDocument();
     });
   });
 
   it('renders mobile calendar tree pane', async () => {
-    render(<CalendarPage />);
+    renderPage();
     expect(screen.getByTestId('mobile-calendar-tree-pane')).toBeInTheDocument();
   });
 
   it('renders mobile calendar view pane only after navigation', async () => {
-    render(<CalendarPage />);
+    renderPage();
     // Mobile view starts on 'tree', so view pane should not be visible initially
     expect(screen.queryByTestId('mobile-calendar-view-pane')).not.toBeInTheDocument();
   });