feat: Absender-Zuordnungen bearbeiten und loeschen

Der Loesch-Endpunkt war da, aber ohne Knopf in der Oberflaeche, und
Bearbeiten fehlte ganz – eine falsch eingetippte Zuordnung liess sich also
nicht mehr korrigieren.

Jede Zuordnung ist jetzt eine eigene Zeile mit Erkennungstext und Konto;
der Speichern-Knopf erscheint erst bei einer Aenderung. Dazu ein PUT auf
/mail/senders/{id} im Backend.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/locales/en.json

@@ -533,6 +533,8 @@
     "skippedTitle": "These emails were skipped",
     "skippedHint": "No sender mapping matched them. Enter part of the address or the subject below and they will be picked up on the next fetch.",
     "fetchedNone": "No emails found in the selected folder. Is the folder right? The first fetch looks at the last 14 days.",
-    "senderHint": "Searched in sender, subject and the start of the body. That way it also works for forwarded emails, where the sender is your own address."
+    "senderHint": "Searched in sender, subject and the start of the body. That way it also works for forwarded emails, where the sender is your own address.",
+    "deleteSender": "Remove mapping",
+    "deleteSenderConfirm": "Remove mapping “{{text}}”? Payments already captured stay."
   }
 }