feat(demo): add Demo Guide (8-step guided tour) and scenario overview

Adds a compact "Probeer een demonstratiescenario" page listing the 5 named
scenarios with live readiness from the manifest, plus a Demo Guide side
panel (bottom sheet on mobile) that walks an Operations Manager through
all 8 steps with per-step context, live-resolved routes, sessionStorage
progress, and a "Demo opnieuw voorbereiden" restart. Login's guided-demo
CTA now actually opens the guide. Fixes a real mobile topbar overflow the
new guide trigger introduced.

frontend/src/components/Layout.tsx

@@ -5,6 +5,7 @@ import { useAuth } from "../context/AuthContext";
 import type { Role, SearchResultItem } from "../api/types";
 import { BrandMark, Icon, type IconName } from "./Icons";
 import { DemoBadge } from "./DemoBadge";
+import { DemoGuide, DemoGuideTrigger } from "./DemoGuide";
 import { useDemoManifest } from "../context/DemoManifestContext";
 
 const SEARCH_ICON: Record<SearchResultItem["type"], IconName> = {
@@ -277,6 +278,7 @@ export function Layout() {
             )}
           </div>
           <div className="topbar-meta">
+            <DemoGuideTrigger />
             <DemoBadge />
             <span className="timezone"><Icon name="clock" /> Europe/Brussels</span>
             {user && (
@@ -307,6 +309,8 @@ export function Layout() {
           <span>More</span>
         </button>
       </nav>
+
+      <DemoGuide />
     </div>
   );
 }