feat(260929-if2): Erinnerung zusaetzlich per E-Mail, Doku und Aenderungsliste

- E-Mail-Planer: Anspruch vor dem Senden (genau eine Mail je Faelligkeit, hoechstens 3 Versuche), Systemlesen nur fuer die Kandidatenabfrage
- MailService.sendReminderEmail (Berliner Zeit, nur Text), GET /reminders/email-status, Haken im Formular mit Erklaerung
- Zugriffsklassifikation und Erlaubnisliste fuer forSystem nachgezogen, Aenderungsliste und Anwenderanleitung

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -508,6 +508,10 @@
       "alreadyDue": "The reminder is now due and can no longer be edited.",
       "notDue": "The reminder is not due yet.",
       "permissionDenied": "Your browser blocks notifications. Due reminders will then only appear here in the tile.",
+      "emailLabel": "Also remind me by e-mail",
+      "emailNoSmtp": "E-mail reminders are not possible because no e-mail delivery is set up. Please contact your administrator.",
+      "emailNoAddress": "Your account has no e-mail address on file.",
+      "emailOn": "Also by e-mail",
       "notificationTitle": "Reminder: {title}"
     },
     "editShort": "Edit",