fix(calendar): EWS uses NTLM auth + edit form stays open after save

- Replace ews-javascript-api (Basic Auth only) with httpntlm for EWS connections
- testEwsConnection uses GetFolder SOAP via NTLM
- fetchViaEws uses FindItem CalendarView SOAP via NTLM
- Edit form no longer auto-closes on save — shows "Erfolgreich gespeichert" instead
- Test button in edit mode uses saved credentials via /sources/:id/test endpoint
- Add saveSuccess i18n key (de/en)

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

apps/web/src/messages/de.json

@@ -209,6 +209,7 @@
       "formTestSuccess": "Verbindung erfolgreich",
       "formTestFailed": "Verbindung fehlgeschlagen",
       "saveError": "Speichern fehlgeschlagen. Bitte Eingaben prüfen.",
+      "saveSuccess": "Erfolgreich gespeichert",
       "formSave": "Speichern",
       "formSaving": "Wird gespeichert...",
       "formCancel": "Abbrechen",