T08b: Frontend Calendar UI (month view, kanban, ICS, resources, sharing)

- 8 calendar components (MonthView, KanbanBoard, AppointmentModal, TaskDetailPanel, IcsControls, ResourceBooking, SharingSettings + API client)

- 2 pages (/calendar, /calendar/kanban) + zustand store

- 17 vitest tests (MonthView 5, KanbanBoard 6, AppointmentModal 6) all passing

- i18n: calendar namespace in en/de (104 lines each, +exportSuccess key)

- TS strict mode pass, npm run build pass

frontend/src/routes/index.tsx

@@ -18,6 +18,8 @@ import { SettingsPage } from '@/pages/Settings';
 import { SettingsProfilePage } from '@/pages/SettingsProfile';
 import { SettingsRolesPage } from '@/pages/SettingsRoles';
 import { SettingsUsersPage } from '@/pages/SettingsUsers';
+import { CalendarPage } from '@/pages/Calendar';
+import { CalendarKanbanPage } from '@/pages/CalendarKanban';
 
 const router = createBrowserRouter([
   {
@@ -51,6 +53,8 @@ const router = createBrowserRouter([
       { path: '/contacts/:id/edit', element: <ContactFormPage /> },
       { path: '/audit-log', element: <AuditLogPage /> },
       { path: '/search', element: <GlobalSearchResultsPage /> },
+      { path: '/calendar', element: <CalendarPage /> },
+      { path: '/calendar/kanban', element: <CalendarKanbanPage /> },
       {
         path: '/settings',
         element: <SettingsPage />,