test(demo): add full guided-demo walkthrough and targeted demo tests

Adds one comprehensive Playwright test that walks a fresh Operations
Manager session through all 8 Demo Guide steps performing the real
action at each one, then restores the environment. Writing it surfaced
a real desktop layout bug: the Demo Guide's fixed side panel overlapped
main content with no reflow, making the return form's "Review return"
button unclickable while the guide was open at ordinary viewport widths.
Fixed by reserving layout space via a guide-open class. Also adds mobile
bottom-sheet, keyboard-reachability, and console-error checks.

frontend/src/components/Layout.tsx

@@ -6,6 +6,7 @@ import type { Role, SearchResultItem } from "../api/types";
 import { BrandMark, Icon, type IconName } from "./Icons";
 import { DemoBadge } from "./DemoBadge";
 import { DemoGuide, DemoGuideTrigger } from "./DemoGuide";
+import { useDemoGuide } from "../context/DemoGuideContext";
 import { useDemoManifest } from "../context/DemoManifestContext";
 
 const SEARCH_ICON: Record<SearchResultItem["type"], IconName> = {
@@ -46,6 +47,7 @@ const NAV_GROUPS: Array<{ label: string; items: NavItem[] }> = [
 export function Layout() {
   const { user, logout } = useAuth();
   const { manifest } = useDemoManifest();
+  const { open: guideOpen } = useDemoGuide();
   const navigate = useNavigate();
   const [mobileOpen, setMobileOpen] = useState(false);
   const [searchQuery, setSearchQuery] = useState("");
@@ -220,7 +222,7 @@ export function Layout() {
 
       {mobileOpen && <button className="nav-scrim" aria-label="Close navigation" onClick={() => setMobileOpen(false)} />}
 
-      <div className="app-workspace">
+      <div className={`app-workspace ${guideOpen ? "guide-open" : ""}`}>
         <header className="topbar">
           <button className="icon-button mobile-menu" type="button" onClick={() => setMobileOpen(true)} aria-label="Open navigation">
             <Icon name="menu" />