feat: Kontenreihenfolge selbst bestimmen

Die Liste stand in der Anlegereihenfolge, die selten die gewuenschte ist.
Neuer Endpunkt PUT /accounts/order nimmt die IDs in der gewuenschten Folge
und schreibt die Position; er muss vor /{account_id} stehen, sonst faengt
die ID-Route den Pfad ab. Fremde IDs werden abgewiesen.

In der Kontenliste zwei Pfeile je Zeile, optimistisch sortiert, damit die
Liste beim Klicken nicht springt.

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

web/src/locales/en.json

@@ -167,7 +167,9 @@
     "empty": "No accounts yet. Create your first account.",
     "deleteConfirm": "Delete this account and all its transactions?",
     "openingDateHint": "Balance at the end of that day. Bookings up to then don't count toward the balance but stay in the list and reports. Without a date, everything counts.",
-    "shortIdentWarning": "Short match texts hit unrelated bookings: “Euro” also occurs in “Europa-Park” or “PayPal Europe”, turning those into transfers by mistake. Prefer something unique such as the IBAN."
+    "shortIdentWarning": "Short match texts hit unrelated bookings: “Euro” also occurs in “Europa-Park” or “PayPal Europe”, turning those into transfers by mistake. Prefer something unique such as the IBAN.",
+    "moveUp": "Move up",
+    "moveDown": "Move down"
   },
   "accountTypes": {
     "girokonto": "Checking",