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.

backend/app/core/config.py

@@ -32,6 +32,9 @@ class Settings(BaseSettings):
     mcp_hub_service_token: str = "replace-me-mcp-hub-token"
     mcp_hub_registration_enabled: bool = False
     cors_allow_origins: str = "http://localhost:1228"
+    demo_organization_name: str = "Northstar Mobility"
+    demo_timezone: str = "Europe/Brussels"
+    demo_allow_reset: bool = True
 
 
 @lru_cache