T08c: Frontend Mail UI + Global Search UI — 44 tests, tsc clean, vite build pass

- Mail page: 3-pane layout (folder tree + mail list + reading pane)
- Compose modal: rich text editor (bold/italic/link), template picker, reply/forward pre-fill
- Mail settings: accounts, signatures, rules, labels, vacation, PGP (6 tabs)
- Shared mailbox selector: switch between personal + shared accounts
- Mail search bar + attachment download + create-event-from-mail
- Global search: tabs for companies/contacts/mails/files/events
- Search autocomplete in TopBar (existing SearchDropdown)
- API client: mail.ts (all endpoints)
- Routes: /mail, /mail/settings
- i18n: de.json + en.json mail + search translations
- 44 new tests (4 test files), full regression 318/318 pass
- tsc --noEmit: 0 errors, vite build: 267 modules

frontend/src/routes/index.tsx

@@ -22,6 +22,8 @@ import { CalendarPage } from '@/pages/Calendar';
 import { CalendarKanbanPage } from '@/pages/CalendarKanban';
 import { DmsPage } from '@/pages/Dms';
 import { DmsTrashPage } from '@/pages/DmsTrash';
+import { MailPage } from '@/pages/Mail';
+import { MailSettingsPage } from '@/pages/MailSettings';
 
 const router = createBrowserRouter([
   {
@@ -59,6 +61,8 @@ const router = createBrowserRouter([
       { path: '/calendar/kanban', element: <CalendarKanbanPage /> },
       { path: '/dms', element: <DmsPage /> },
       { path: '/dms/trash', element: <DmsTrashPage /> },
+      { path: '/mail', element: <MailPage /> },
+      { path: '/mail/settings', element: <MailSettingsPage /> },
       {
         path: '/settings',
         element: <SettingsPage />,