feat(demo): plain-language integration status, richer audit, reset integrity

Integration status badges across Dashboard/Automation now show honest
plain-language labels instead of raw backend state strings (and fix a
few states that had no matching CSS colour class at all). Audit trail
gets a "view related events" action reusing the existing correlation_id
filter. About page gains scope/architecture/security/testing sections
and a guided-demo entry point. POST /api/v1/demo/reset now runs and
records a server-side scenario-integrity check. Also fixes a second real
race condition (caught by the return-review e2e test): the odometer
scenario pre-fill now resolves before ReturnForm mounts instead of
patching its value in after the fact.

frontend/src/pages/BookingDetail.tsx

@@ -84,7 +84,14 @@ export function BookingDetail() {
       )}
 
       {returnResult && <ReturnResultPanel result={returnResult} />}
-      {!returnResult && booking.status === "active" && (
+      {/* Wait for the scenario's canonical odometer before mounting the form at all when
+          this is the known demo scenario, so ReturnForm's suggestedOdometerKm is correct
+          from its very first render -- never updated asynchronously after mount, which
+          previously raced with anyone already typing into the field. */}
+      {!returnResult && booking.status === "active" && isReturnAnomalyScenario && canonicalOdometerKm === null && (
+        <LoadingState label="Scenario voorbereiden…" />
+      )}
+      {!returnResult && booking.status === "active" && (!isReturnAnomalyScenario || canonicalOdometerKm !== null) && (
         <ReturnForm
           bookingRef={booking.public_ref}
           onRegistered={handleRegistered}