feat(demo): add demo manifest, Dutch demo entry, permanent badge and About page

Adds GET /api/v1/demo/manifest as a single source of truth for the demo's
fictional org identity (Northstar Mobility -- surfacing the project's
already-locked tenant name), synthetic-data/reset state, and live scenario
readiness. Rewrites the login screen in Dutch with an honest, no-password
demo entry and a guided-demo entry point, replaces the loud full-width
demo banner with a subtle badge + popover, and adds a compact About page
explaining what's real vs. synthetic vs. not yet connected.

frontend/src/api/types.ts

@@ -252,6 +252,40 @@ export interface IntegrationStatus {
   mcp_hub: McpHubIntegrationStatus;
 }
 
+export interface DemoScenario {
+  id: string;
+  title: string;
+  operational_problem: string;
+  estimated_minutes: number;
+  required_roles: Role[];
+  start_path: string;
+  demonstrates: string;
+  ready: boolean;
+  blocked_reason: string | null;
+}
+
+export interface DemoIntegrationSummary {
+  key: "n8n" | "ragcore" | "mcp_hub";
+  label: string;
+  status_label: string;
+  detail: string;
+}
+
+export interface DemoManifest {
+  demo_mode: boolean;
+  organization_name: string;
+  organization_description: string;
+  timezone: string;
+  synthetic_data: boolean;
+  allow_reset: boolean;
+  last_reset_at: string | null;
+  anchor_date: string | null;
+  guide_available: boolean;
+  required_roles: Role[];
+  scenarios: DemoScenario[];
+  integrations: DemoIntegrationSummary[];
+}
+
 export interface AuditEvent {
   id: string;
   actor_type: string;