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/crowd-lists/CrowdListDetailPanel.vue

@@ -68,7 +68,7 @@ const filteredPersons = computed(() => {
   if (searchQuery.value) {
     const q = searchQuery.value.toLowerCase()
     result = result.filter(
-      (p: Person) => p.name.toLowerCase().includes(q) || p.email.toLowerCase().includes(q),
+      (p: Person) => p.full_name.toLowerCase().includes(q) || p.email.toLowerCase().includes(q),
     )
   }
 
@@ -181,7 +181,7 @@ function getInitials(name: string) {
 function onApprove(person: Person) {
   approvePerson(person.id, {
     onSuccess: () => {
-      successMessage.value = `${person.name} goedgekeurd`
+      successMessage.value = `${person.full_name} goedgekeurd`
       showSuccess.value = true
       refetchPersons()
     },
@@ -195,7 +195,7 @@ function onRemoveConfirm(person: Person) {
 
 function onRemoveExecute() {
   if (!removingPerson.value || !props.crowdList) return
-  const name = removingPerson.value.name
+  const name = removingPerson.value.full_name
 
   removePerson(
     { listId: props.crowdList.id, personId: removingPerson.value.id },
@@ -613,11 +613,11 @@ function onApproveAllExecute() {
                     color="primary"
                     variant="tonal"
                   >
-                    <span class="text-caption">{{ getInitials(person.name) }}</span>
+                    <span class="text-caption">{{ getInitials(person.full_name) }}</span>
                   </VAvatar>
                   <div style="min-width: 0;">
                     <p class="text-body-1 font-weight-medium mb-0 text-truncate">
-                      {{ person.name }}
+                      {{ person.full_name }}
                     </p>
                     <p class="text-body-2 text-medium-emphasis mb-1 text-truncate">
                       {{ person.email }}
@@ -715,7 +715,7 @@ function onApproveAllExecute() {
     >
       <VCard title="Persoon verwijderen van lijst">
         <VCardText>
-          Weet je zeker dat je <strong>{{ removingPerson?.name }}</strong> van de lijst
+          Weet je zeker dat je <strong>{{ removingPerson?.full_name }}</strong> van de lijst
           <strong>{{ crowdList?.name }}</strong> wilt verwijderen?
           <br><br>
           <span class="text-medium-emphasis">