fix: Hinweis nannte das falsche Erkennungsmerkmal fuer die Sandbox

Der Text riet, auf "Test- oder Mock-Institute" zu achten. Das ist falsch und
hat die Fehlersuche in die Irre gefuehrt: Die Sandbox-Liste enthaelt echte
Banknamen wie "Aachener Bank" und "Nordea" – nur N26 und Revolut fehlen. Wer
echte Namen sieht, schliesst die Sandbox faelschlich aus.

Jetzt verweist der Hinweis auf die Zeile "Environment" im Control Panel, wo
SANDBOX oder PRODUCTION eindeutig dabeisteht. Die Einrichtungsanleitung sagt
ausserdem gleich beim Anlegen, dass PRODUCTION gewaehlt werden muss.

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

web/src/locales/en.json

@@ -568,7 +568,7 @@
     "setupTitle": "One-time setup",
     "setupHint": "You need your own Enable Banking application. It cannot ship with Certain – the key is bound to your registration.",
     "setupStep1": "Sign in at enablebanking.com (the account is created on first sign-in).",
-    "setupStep2": "Create a Production application and download the key file (.pem). It becomes active once you link your own accounts.",
+    "setupStep2": "Create an application and be sure to choose PRODUCTION, not Sandbox – the sandbox knows neither N26 nor Revolut. Then download the key file (.pem).",
     "setupStep3": "Enter this address there as the redirect URL:",
     "setupStart": "Enter credentials",
     "appTitle": "Enable Banking credentials",
@@ -605,10 +605,10 @@
     "noMatch": "{{gesamt}} banks loaded, but none matches. Try something shorter – some are listed under a different name than the one you know.",
     "noneLoaded": "The interface returned no banks at all. That is not the search term: check whether your Enable Banking application is active yet – it only becomes active once you have linked your own accounts there.",
     "sampleTitle": "Examples from across the loaded list:",
-    "sandboxHint": "If those are test or mock institutions instead of real banks, your application is registered as “Sandbox” in the Control Panel. N26 and Revolut exist only in “Production”, where they are listed under exactly those names.",
+    "sandboxHint": "If your bank is missing, check the “Environment” line under “API applications” in the Control Panel. If it says SANDBOX, that is the cause: the sandbox list contains real bank names such as “Aachener Bank” or “Nordea”, but neither N26 nor Revolut. You need a PRODUCTION application for those.",
     "range": "The list runs from “{{von}}” to “{{bis}}”.",
     "letters": "Initial letters present",
-    "truncatedHint": "If whole letters are missing – N or R, say – the list is truncated and your bank was never delivered. Then the search term is innocent and the query needs paging.",
+    "truncatedHint": "If whole letters are missing, the list is incomplete. If only your bank is missing, check below what is listed under the same initial letter.",
     "sameLetter": "Everything in the list starting with “{{buchstabe}}”:",
     "pickBankMore": "The best {{n}} of {{treffer}} matches – search more precisely if yours is not among them:"
   },