feat: split name into first_name + last_name across users, persons, and companies

Cross-cutting migration affecting the entire stack:
- Database: 3 migrations splitting name columns with data migration
- Models: first_name/last_name on User, Person; contact_first_name/contact_last_name on Company; backward-compatible name accessors
- API: all resources return first_name, last_name, full_name; assignablePersons endpoint updated
- Requests: validation rules updated for all person/user/company forms
- Services: VolunteerRegistrationService, ShiftAssignmentService, InvitationService updated
- Frontend: TypeScript types, Zod schemas, all forms split into Voornaam/Achternaam fields
- Display: all person/user name references use full_name; initials use first_name[0]+last_name[0]
- Tests: all 371 tests passing
- Docs: SCHEMA.md and API.md updated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/app/src/components/events/EventTabsNav.vue

@@ -4,6 +4,7 @@ import { dutchPlural } from '@/lib/dutch-plural'
 import { useAuthStore } from '@/stores/useAuthStore'
 import { useOrganisationStore } from '@/stores/useOrganisationStore'
 import EditEventDialog from '@/components/events/EditEventDialog.vue'
+import RegistrationLinkCard from '@/components/events/RegistrationLinkCard.vue'
 import type { EventStatus } from '@/types/event'
 
 const route = useRoute()
@@ -177,6 +178,12 @@ const backRoute = computed(() => {
         </VBtn>
       </div>
 
+      <!-- Registration link (top-level events only) -->
+      <RegistrationLinkCard
+        v-if="!event.parent_event_id"
+        :event="event"
+      />
+
       <!-- Horizontal tabs -->
       <VTabs
         :model-value="activeTab"