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.

.env.example

@@ -14,6 +14,13 @@ TZ=Europe/Brussels
 # otherwise browsers will silently drop the cookie and no one can log in.
 SESSION_COOKIE_SECURE=false
 
+# Demo presentation (fictional org identity, badge/manifest, reset safety valve).
+# DEMO_ALLOW_RESET=false permanently disables POST /api/v1/demo/reset (403), independent
+# of role -- a safety valve for any environment where the dataset must not be rebuildable.
+DEMO_ORGANIZATION_NAME=Northstar Mobility
+DEMO_TIMEZONE=Europe/Brussels
+DEMO_ALLOW_RESET=true
+
 # n8n
 N8N_BASE_URL=http://n8n:5678
 N8N_WEBHOOK_URL=http://n8n:5678/webhook/mobilityops-return