feat: Umsaetze je Konto holen, Takt fuer den automatischen Abruf

Drei Sachen an der Bankanbindung.

'Umsaetze holen' lief ueber alle Konten einer Verbindung. Seit angebundene
Konten selbst buchen, ist ein Klick damit folgenreich: Er bucht auf zwei
Konten. Der Knopf sitzt jetzt in der Kontozeile; an der Verbindung bleibt
'Alle Konten holen'.

Dabei musste der Zeitstempel mitwandern. last_sync_at hing an der
Verbindung – ein Einzelabruf haette damit das Startdatum der uebrigen Konten
mit vorgeschoben, und deren Umsaetze aus dem uebersprungenen Zeitraum waeren
nie angekommen. Der Stempel gehoert an das Konto, das abgerufen wurde.

Neu ist ein Takt je Verbindung, nach demselben Muster wie beim Postfach: ein
Hintergrund-Thread, der jede Minute nachsieht, ob etwas faellig ist. Bewusst
ein eigener Thread – ein haengender Bankzugang darf den Mail-Abruf nicht
mitreissen. Die Vorgabe ist 0, also aus: Anders als beim Mail-Abruf entstehen
hier Buchungen, das laeuft nicht ungefragt los. Schlaegt ein Abruf fehl, wird
der Stempel trotzdem gesetzt, sonst liefe die Verbindung jede Minute in
denselben Fehler.

Und die Abschnitte heissen jetzt 'Bankkonten Anbindung' und 'Mail Import'.

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

web/src/locales/en.json

@@ -528,7 +528,7 @@
     "transferBooked": "Booked as a transfer."
   },
   "mailbox": {
-    "title": "Mailbox for payment emails",
+    "title": "Mail import",
     "intro": "Raiffeisen and Revolut send an email for transfers. Certain fetches them and puts them into the inbox as suggestions – only what you approve gets booked. Card payments in a shop are not emailed by the banks; use the shortcut capture under “My account” for those.",
     "add": "Add mailbox",
     "name": "Label",
@@ -572,7 +572,7 @@
     "anyCurrency": "any currency"
   },
   "bank": {
-    "title": "Connect bank accounts directly",
+    "title": "Bank account connection",
     "intro": "Under PSD2, EU banks must offer an interface – but only to licensed services. Enable Banking holds that licence and passes it on, so N26 and Revolut can be read directly, without CSV. Switzerland is not covered by PSD2; Raiffeisen stays on file import.",
     "setupTitle": "One-time setup",
     "setupHint": "You need your own Enable Banking application. It cannot ship with Certain – the key is bound to your registration.",
@@ -597,10 +597,9 @@
     "notMapped": "not mapped to an account yet",
     "mapHint": "Without a mapping nothing is fetched from this account.",
     "noAccountsFound": "No accounts were returned. In restricted mode the bank only releases what you linked at Enable Banking under “Activate by linking accounts” – add this bank there and reconnect here.",
-    "sync": "Fetch transactions",
     "synced": "{{gebucht}} transactions booked (from {{ab}}).",
     "noMapping": "No account mapped – map one above first, then it will fetch.",
-    "lastSync": "last fetched on {{datum}}",
+    "lastSync": "last {{when}}",
     "neverSynced": "never fetched",
     "lastError": "Error",
     "validUntil": "Consent valid until {{datum}}",
@@ -629,7 +628,13 @@
     "balancesFetched": "{{n}} balances updated.",
     "syncedPending": "{{n}} pending – they arrive once the bank books them.",
     "syncedTransfers": "{{n}} connected as transfers.",
-    "syncHint": "Transactions from connected accounts are booked directly – the balance then matches by itself. What remains is assigning a category."
+    "syncHint": "Transactions from connected accounts are booked directly – the balance then matches by itself. What remains is assigning a category.",
+    "syncAll": "Fetch all accounts",
+    "syncOne": "Fetch transactions",
+    "poll": "Fetch automatically",
+    "pollUnit": "minutes (0 = off)",
+    "pollHint": "Certain then fetches and books transactions on its own. 0 turns this off; banks do not allow less than 15 minutes.",
+    "pollSaved": "Interval saved."
   },
   "bankReturn": {
     "title": "Back from your bank",