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__/ai/SessionList.test.tsx

@@ -1,8 +1,19 @@
 import React from 'react';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { SessionList } from '@/components/ai/SessionList';
 
+const queryClient = new QueryClient({
+  defaultOptions: { queries: { retry: false } },
+});
+
+function renderWithProvider(ui: React.ReactElement) {
+  return render(
+    <QueryClientProvider client={queryClient}>{ui}</QueryClientProvider>
+  );
+}
+
 const mockSessions = [
   { id: 's1', title: 'First Chat', folder_id: null, agent_id: null, is_sidebar: false, created_at: '2024-01-01T00:00:00Z', updated_at: '2024-01-01T00:00:00Z' },
   { id: 's2', title: 'Second Chat', folder_id: 'f1', agent_id: null, is_sidebar: false, created_at: '2024-01-01T00:00:00Z', updated_at: '2024-01-01T00:00:00Z' },
@@ -46,21 +57,21 @@ beforeEach(() => {
 
 describe('SessionList', () => {
   it('renders session list with sessions', async () => {
-    render(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
+    renderWithProvider(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
     await waitFor(() => {
       expect(screen.getByText('First Chat')).toBeInTheDocument();
     });
   });
 
   it('renders folder names', async () => {
-    render(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
+    renderWithProvider(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
     await waitFor(() => {
       expect(screen.getByText('My Folder')).toBeInTheDocument();
     });
   });
 
   it('renders sessions inside folders', async () => {
-    render(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
+    renderWithProvider(<SessionList activeSessionId="s1" onSelectSession={vi.fn()} />);
     await waitFor(() => {
       expect(screen.getByText('Second Chat')).toBeInTheDocument();
     });
@@ -68,7 +79,7 @@ describe('SessionList', () => {
 
   it('calls onSelectSession when session clicked', async () => {
     const onSelect = vi.fn();
-    render(<SessionList activeSessionId={null} onSelectSession={onSelect} />);
+    renderWithProvider(<SessionList activeSessionId={null} onSelectSession={onSelect} />);
     await waitFor(() => {
       expect(screen.getByText('First Chat')).toBeInTheDocument();
     });
@@ -79,13 +90,13 @@ describe('SessionList', () => {
   it('shows loading state initially', () => {
     fetchSessionsMock.mockReturnValue(new Promise(() => {}));
     fetchFoldersMock.mockReturnValue(new Promise(() => {}));
-    render(<SessionList activeSessionId={null} onSelectSession={vi.fn()} />);
+    renderWithProvider(<SessionList activeSessionId={null} onSelectSession={vi.fn()} />);
     expect(screen.getByText('Laden...')).toBeInTheDocument();
   });
 
   it('displays error when fetch fails', async () => {
     fetchSessionsMock.mockRejectedValueOnce(new Error('Failed to load'));
-    render(<SessionList activeSessionId={null} onSelectSession={vi.fn()} />);
+    renderWithProvider(<SessionList activeSessionId={null} onSelectSession={vi.fn()} />);
     await waitFor(() => {
       expect(screen.getByText('Failed to load')).toBeInTheDocument();
     });