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/shifts/ShiftDetailPanel.vue

@@ -75,7 +75,7 @@ async function executeReassign(assignment: ShiftAssignment) {
       shiftId: assignment.shift_id,
       personId: assignment.person_id,
     })
-    successMessage.value = `${assignment.person?.name ?? 'Persoon'} opnieuw toegewezen`
+    successMessage.value = `${assignment.person?.full_name ?? 'Persoon'} opnieuw toegewezen`
     showSuccess.value = true
   }
   catch {
@@ -186,7 +186,7 @@ const successMessage = ref('')
 function onApprove(assignment: ShiftAssignment) {
   approveAssignment(assignment.id, {
     onSuccess: () => {
-      successMessage.value = `${assignment.person?.name ?? 'Toewijzing'} goedgekeurd`
+      successMessage.value = `${assignment.person?.full_name ?? 'Toewijzing'} goedgekeurd`
       showSuccess.value = true
     },
   })
@@ -199,7 +199,7 @@ function onCancel(assignment: ShiftAssignment) {
 
 function onCancelExecute() {
   if (!cancellingAssignment.value) return
-  const name = cancellingAssignment.value.person?.name ?? 'Toewijzing'
+  const name = cancellingAssignment.value.person?.full_name ?? 'Toewijzing'
 
   cancelAssignment(cancellingAssignment.value.id, {
     onSuccess: () => {
@@ -224,7 +224,7 @@ function onReject(assignment: ShiftAssignment) {
 
 function onRejectExecute() {
   if (!rejectingAssignment.value) return
-  const name = rejectingAssignment.value.person?.name ?? 'Toewijzing'
+  const name = rejectingAssignment.value.person?.full_name ?? 'Toewijzing'
 
   rejectAssignment(
     {
@@ -644,14 +644,14 @@ function fillRateColor(): string {
                       variant="tonal"
                     >
                       <span class="text-caption">
-                        {{ assignment.person ? getInitials(assignment.person.name) : '?' }}
+                        {{ assignment.person ? getInitials(assignment.person.full_name) : '?' }}
                       </span>
                     </VAvatar>
 
                     <div style="min-width: 0;" class="flex-grow-1">
                       <div class="d-flex align-center gap-x-2 flex-wrap">
                         <span class="text-body-2 font-weight-medium text-truncate">
-                          {{ assignment.person?.name ?? 'Onbekend' }}
+                          {{ assignment.person?.full_name ?? 'Onbekend' }}
                         </span>
                         <VChip
                           v-if="assignment.status === ShiftAssignmentStatus.REJECTED"
@@ -775,7 +775,7 @@ function fillRateColor(): string {
       <VCard title="Toewijzing afwijzen">
         <VCardText>
           Weet je zeker dat je de toewijzing van
-          <strong>{{ rejectingAssignment?.person?.name ?? 'deze persoon' }}</strong>
+          <strong>{{ rejectingAssignment?.person?.full_name ?? 'deze persoon' }}</strong>
           wilt afwijzen?
 
           <VTextarea
@@ -814,7 +814,7 @@ function fillRateColor(): string {
       <VCard title="Toewijzing annuleren">
         <VCardText>
           Weet je zeker dat je de toewijzing van
-          <strong>{{ cancellingAssignment?.person?.name ?? 'deze persoon' }}</strong>
+          <strong>{{ cancellingAssignment?.person?.full_name ?? 'deze persoon' }}</strong>
           wilt annuleren?
         </VCardText>
         <VCardActions>
@@ -877,7 +877,7 @@ function fillRateColor(): string {
           Vrijwilliger opnieuw toewijzen?
         </VCardTitle>
         <VCardText class="px-5">
-          <strong>{{ reassigningAssignment?.person?.name ?? 'Deze persoon' }}</strong>
+          <strong>{{ reassigningAssignment?.person?.full_name ?? 'Deze persoon' }}</strong>
           heeft zichzelf afgemeld voor deze shift. Weet je zeker dat je deze
           persoon opnieuw wilt toewijzen?
         </VCardText>