feat(5.21): Tasks Plugin — activities with status, priority, due dates, ARQ reminders

- New builtin plugin app/plugins/builtins/tasks/ with full CRUD
- Task model with TenantMixin (title, description, status, priority, due_date, assigned_to, contact_id)
- Routes: GET/POST /tasks, GET/PATCH/DELETE /tasks/{id}, POST /tasks/{id}/assign, POST /tasks/{id}/status
- All routes RBAC-protected (tasks:read, tasks:write, tasks:delete)
- ARQ cron job tasks_due_reminder (daily 8:00) sends notifications for due tasks
- Migration 0001_initial.sql creates tasks table with indexes
- Frontend: Tasks.tsx page with list, filter, create/edit modal, detail modal
- Frontend: api/tasks.ts with React Query hooks
- Route /tasks in routes/index.tsx, sidebar entry via plugin manifest
- i18n keys for nav.tasks and tasks.* in de.json and en.json
- Tests: test_tasks.py (11 tests) + Tasks.test.tsx (3 tests)
- Registered TasksPlugin in conftest.py and worker.py

frontend/src/__tests__/Tasks.test.tsx

@@ -0,0 +1,134 @@
+/**
+ * Tasks page tests — basic rendering and interaction.
+ */
+
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
+import { TasksPage } from '@/pages/Tasks';
+import * as tasksApi from '@/api/tasks';
+
+// Mock i18n
+vi.mock('react-i18next', () => ({
+  useTranslation: () => ({ t: (key: string) => key }),
+}));
+
+// Mock toast
+vi.mock('@/components/ui/Toast', () => ({
+  useToast: () => ({
+    success: vi.fn(),
+    error: vi.fn(),
+    warning: vi.fn(),
+    info: vi.fn(),
+  }),
+}));
+
+// Mock UI components
+vi.mock('@/components/ui/Input', () => ({
+  Input: ({ value, onChange, type, label, ...props }: any) => (
+    <div>
+      {label && <label>{label}</label>}
+      <input
+        data-testid={props['data-testid'] || 'input'}
+        type={type || 'text'}
+        value={value || ''}
+        onChange={onChange}
+      />
+    </div>
+  ),
+}));
+
+vi.mock('@/components/ui/Select', () => ({
+  Select: ({ value, onChange, options, label, ...props }: any) => (
+    <div>
+      {label && <label>{label}</label>}
+      <select data-testid={props['data-testid'] || 'select'} value={value || ''} onChange={onChange}>
+        {options?.map((o: any) => <option key={o.value} value={o.value}>{o.label}</option>)}
+      </select>
+    </div>
+  ),
+}));
+
+vi.mock('@/components/ui/Modal', () => ({
+  Modal: ({ open, onClose, title, children }: any) =>
+    open ? (
+      <div data-testid="modal" role="dialog">
+        <h2>{title}</h2>
+        <button onClick={onClose}>Close</button>
+        {children}
+      </div>
+    ) : null,
+}));
+
+vi.mock('@/components/ui/Button', () => ({
+  Button: ({ children, onClick, disabled, ...props }: any) => (
+    <button onClick={onClick} disabled={disabled} data-testid={props['data-testid'] || 'button'}>
+      {children}
+    </button>
+  ),
+}));
+
+vi.mock('@/components/ui/Badge', () => ({
+  Badge: ({ children, variant }: any) => <span data-testid="badge" data-variant={variant}>{children}</span>,
+}));
+
+vi.mock('@/components/ui/EmptyState', () => ({
+  EmptyState: ({ title, description }: any) => (
+    <div data-testid="empty-state">
+      <h3>{title}</h3>
+      <p>{description}</p>
+    </div>
+  ),
+}));
+
+// Mock tasks API
+vi.mock('@/api/tasks', () => ({
+  useTasks: vi.fn(() => ({
+    data: {
+      items: [
+        {
+          id: 'task-1',
+          title: 'Test Task',
+          description: 'Test description',
+          status: 'open',
+          priority: 'high',
+          due_date: '2025-12-31T10:00:00Z',
+          assigned_to: null,
+          contact_id: null,
+          created_by: null,
+          created_at: '2025-01-01T00:00:00Z',
+          updated_at: '2025-01-01T00:00:00Z',
+        },
+      ],
+      total: 1,
+      page: 1,
+      page_size: 25,
+    },
+    isLoading: false,
+  })),
+  useCreateTask: vi.fn(() => ({ mutateAsync: vi.fn() })),
+  useUpdateTask: vi.fn(() => ({ mutateAsync: vi.fn() })),
+  useDeleteTask: vi.fn(() => ({ mutateAsync: vi.fn() })),
+  useUpdateTaskStatus: vi.fn(() => ({ mutateAsync: vi.fn() })),
+}));
+
+describe('TasksPage', () => {
+  it('renders the tasks page with header', () => {
+    render(<TasksPage />);
+    expect(screen.getByTestId('tasks-page')).toBeInTheDocument();
+    expect(screen.getByText('tasks.title')).toBeInTheDocument();
+  });
+
+  it('renders task items from API', () => {
+    render(<TasksPage />);
+    expect(screen.getByText('Test Task')).toBeInTheDocument();
+    expect(screen.getByText('Test description')).toBeInTheDocument();
+  });
+
+  it('opens create modal when create button is clicked', () => {
+    render(<TasksPage />);
+    const createBtn = screen.getByText('tasks.create');
+    fireEvent.click(createBtn);
+    expect(screen.getByTestId('modal')).toBeInTheDocument();
+    expect(screen.getByTestId('task-title-input')).toBeInTheDocument();
+  });
+});