fix(event-types): harden setup window + catalog validation (codex review)

Three review rounds on PR #801; fixes in response:

- isValidEventType: live catalog is authoritative when it has rows — a
  deleted or deactivated slug no longer validates via the legacy
  fallback (fallback now only serves an empty-catalog install)
- deleteEventType: refuse deleting the last (and last ACTIVE) type;
  updateEventType: refuse deactivating the last active type (unknown
  slugs are rejected since the validator change, so an empty active
  catalog would brick event creation)
- setup window fails closed: only an explicit stored `false` opens it
  (a portable-backup restore can leave the key absent) and a normal
  admin login durably closes it (abandoned-wizard case)
- reserved bootstrap keys (setup_wizard_completed, setup_token) are
  stripped from ALL generic settings upserts (/general, /security,
  /analytics, /seo) so the marker is genuinely one-way
- wizard step: deletes ordered so the catalog can never end up empty,
  and a genuinely failed system-type deletion reloads the list and
  stays on the step instead of advancing past the only window in which
  it can be retried
- CreateEventPage: snap the hardcoded initial 'wedding' selection to
  the first active type when the catalog no longer contains it
- v1 API: new GET /event-types (read scope) so token clients can
  discover valid slugs; OpenAPI enum replaced with the live-catalog
  description

frontend/src/pages/admin/CreateEventPage.tsx

@@ -182,6 +182,18 @@ export const CreateEventPage: React.FC = () => {
     [eventTypes]
   );
 
+  // The hardcoded initial form value ('wedding') may not exist in the live
+  // catalog — the setup wizard can rename or delete the defaults (#800), and
+  // the backend now rejects unknown slugs. Snap to the first active type; a
+  // user-picked value is always in the list, so this never fights the user.
+  useEffect(() => {
+    if (!availableEventTypes.length) return;
+    if (!availableEventTypes.some(t => t.value === formData.event_type)) {
+      setFormData(prev => ({ ...prev, event_type: availableEventTypes[0].value }));
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [availableEventTypes, formData.event_type]);
+
   // Fetch default settings
   const { data: settings } = useQuery({
     queryKey: ['admin-settings'],