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/e2e/_capture-screenshots.spec.ts

@@ -14,7 +14,7 @@ test("capture the seven main pages", async ({ page, request }) => {
   await page.goto("/login");
   await page.screenshot({ path: `${OUT}/1-login.png` });
 
-  await page.getByRole("button", { name: "Verken als Operations Manager" }).click();
+  await page.getByRole("button", { name: "Verken als Operationsmanager" }).click();
   await expect(page.getByRole("heading", { name: "Operational metrics" })).toBeVisible();
   await page.screenshot({ path: `${OUT}/2-dashboard.png`, fullPage: true });