fix: translate remaining NL/FR interface gaps

Role names, audit/scenario labels, and status text were previously either
left in English or only partially translated:
- auth.json/demo.json role labels actually translated (not just labelled
  as translated): Operationsmanager/Verhuurmedewerker,
  Responsable des operations/Collaborateur de location.
- "Audit trail" -> Auditgeschiedenis/Piste d'audit (title, column header,
  and every mid-sentence occurrence across demo.json, quality.json,
  returns.json -- these embedded leaks were previously invisible to the
  whole-string identity check).
- "Open" (status) -> Openstaand, "Recent" -> Recentste,
  "Start scenario" -> Scenario starten / Demarrer le scenario.

Matching Playwright spec text updated in the same commit so the suite
never regresses through a broken intermediate state.

frontend/src/i18n/locales/nl-BE/auth.json

@@ -9,15 +9,15 @@
   "accessHeading": "Kies hoe je wil starten",
   "accessIntro": "Geen wachtwoord nodig. Elke rol opent een afgebakende, synthetische omgeving — alle workflows en controles zijn echt geïmplementeerd.",
   "startGuidedDemo": "Start begeleide demo",
-  "exploreAsOperationsManager": "Verken als Operations Manager",
+  "exploreAsOperationsManager": "Verken als Operationsmanager",
   "exploreAsOperationsManagerDetail": "Volledig overzicht, kwaliteitsoplossing en herpogingen",
-  "exploreAsRentalEmployee": "Verken als Rental Employee",
+  "exploreAsRentalEmployee": "Verken als Verhuurmedewerker",
   "exploreAsRentalEmployeeDetail": "Boekingen, retours, wagenpark en procedures",
   "safeByDesignTitle": "Veilig ontworpen",
   "safeByDesignDetail": "Elke actie wordt gelogd en is in deze demo herstelbaar.",
   "loginFailed": "De demo-sessie kon niet gestart worden. De API is mogelijk niet bereikbaar.",
-  "roleOperationsManager": "Operations manager",
-  "roleRentalEmployee": "Rental employee",
+  "roleOperationsManager": "Operationsmanager",
+  "roleRentalEmployee": "Verhuurmedewerker",
   "switchRole": "Wissel van rol",
   "logout": "Uitloggen"
 }