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.

backend/app/services/demo_manifest.py

@@ -223,6 +223,20 @@ def _integrations(db: Session) -> list[DemoIntegrationSummaryOut]:
     ]
 
 
+def scenario_integrity_report(db: Session) -> dict:
+    """Server-side scenario-integrity check run after every reset (section 15): confirms
+    each of the 5 named scenarios is actually present and ready, rather than trusting the
+    seed loader silently. Reuses the same readiness derivation the manifest/scenario
+    overview already use, so this can never drift from what a visitor actually sees."""
+    scenarios = _scenarios(db)
+    not_ready = [
+        {"id": s.id, "title": s.title, "reason": s.blocked_reason}
+        for s in scenarios
+        if not s.ready
+    ]
+    return {"all_ready": len(not_ready) == 0, "not_ready": not_ready}
+
+
 def build_demo_manifest(db: Session) -> DemoManifestOut:
     last_reset_at, anchor_date = _last_reset(db)
     return DemoManifestOut(