feat: add daily digest email notification module

- New DailyDigestModule with scheduled summary email for open dashboard items
- Extract StatsService from StatsController for reuse in digest
- Add DailyDigestEnabled, UserEmail, UserPreferredUsername to UserSettings entity
- Sync email/username from OIDC token on each get/update call
- Add dailyDigestEnabled to UserSettingsDto and update API
- Notifications tab in UserSettingsPage with enable toggle and "Jetzt senden" button

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

paperless-frontend/src/api/userSettings.ts

@@ -11,6 +11,7 @@ export interface UserSettingsData {
   mailSignatureHtml: string | null;
   defaultLabelTemplateId: number | null;
   emailRecipientHistory: string[] | null;
+  dailyDigestEnabled: boolean;
 }
 
 export interface SenderOption {
@@ -31,4 +32,7 @@ export const userSettingsApi = {
 
   getSenders: () =>
     api.get<SenderOption[]>('/api/user-settings/senders').then((r) => r.data),
+
+  sendDigestNow: () =>
+    api.post<{ ok: boolean; error?: string }>('/api/daily-digest/send-now').then((r) => r.data),
 };

paperless-frontend/src/pages/UserSettingsPage.tsx

@@ -197,6 +197,71 @@ function MailSettingsTab() {
   );
 }
 
+function NotificationsTab() {
+  const [enabled, setEnabled] = useState(false);
+  const [loading, setLoading] = useState(true);
+  const [saving, setSaving] = useState(false);
+  const [sending, setSending] = useState(false);
+
+  useEffect(() => {
+    userSettingsApi.get()
+      .then((data) => setEnabled(data.dailyDigestEnabled ?? false))
+      .catch(() => message.error('Einstellungen konnten nicht geladen werden'))
+      .finally(() => setLoading(false));
+  }, []);
+
+  const handleSave = async () => {
+    setSaving(true);
+    try {
+      await userSettingsApi.update({ dailyDigestEnabled: enabled });
+      message.success('Einstellungen gespeichert');
+    } catch {
+      message.error('Speichern fehlgeschlagen');
+    } finally {
+      setSaving(false);
+    }
+  };
+
+  const handleSendNow = async () => {
+    setSending(true);
+    try {
+      const result = await userSettingsApi.sendDigestNow();
+      if (result.ok) {
+        message.success('Tagesübersicht wurde gesendet');
+      } else {
+        message.error(result.error ?? 'Senden fehlgeschlagen');
+      }
+    } catch {
+      message.error('Senden fehlgeschlagen');
+    } finally {
+      setSending(false);
+    }
+  };
+
+  if (loading) return null;
+
+  return (
+    <Form layout="vertical" style={{ maxWidth: 600 }}>
+      <Form.Item
+        label="Tägliche E-Mail-Zusammenfassung"
+        extra="Sie erhalten jeden Morgen eine E-Mail mit der Übersicht aller offenen Vorgänge aus dem Dashboard."
+      >
+        <Switch checked={enabled} onChange={setEnabled} />
+      </Form.Item>
+      <Form.Item>
+        <Space>
+          <Button type="primary" loading={saving} onClick={handleSave}>
+            Speichern
+          </Button>
+          <Button loading={sending} onClick={handleSendNow}>
+            Jetzt senden
+          </Button>
+        </Space>
+      </Form.Item>
+    </Form>
+  );
+}
+
 export default function UserSettingsPage() {
   return (
     <div>
@@ -214,6 +279,11 @@ export default function UserSettingsPage() {
               label: 'Etikettendruck',
               children: <LabelSettingsTab />,
             },
+            {
+              key: 'notifications',
+              label: 'Benachrichtigungen',
+              children: <NotificationsTab />,
+            },
           ]}
         />
       </Card>