Help guide opens on demand only; add At the door to admin quick actions

- The site-wide help guide no longer auto-opens on first visit to a page
  — it only opens when the help button is clicked. Removed the
  now-pointless "Don't show this again" checkbox and the per-page
  dismissal tracking it drove.
- Admin dashboard quick actions was missing "At the door" (walk-in
  registration, payments, ticket printing), which Supervisor already had.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/content/help/registry.ts

@@ -28,7 +28,7 @@ import { staffTicketScanningHelpContent } from "./staff-ticket-scanning";
 import { userFormsHelpContent } from "./user-forms";
 
 type HelpRegistryEntry = {
-  /** Unique, stable slug — used as the per-page "don't show again" storage key. */
+  /** Unique, stable identifier for this guide. */
   slug: string;
   matches: (pathname: string) => boolean;
   content: HelpContent;