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>

api/app/Http/Resources/Api/V1/CompanyResource.php

@@ -16,7 +16,9 @@ final class CompanyResource extends JsonResource
             'organisation_id' => $this->organisation_id,
             'name' => $this->name,
             'type' => $this->type,
-            'contact_name' => $this->contact_name,
+            'contact_first_name' => $this->contact_first_name,
+            'contact_last_name' => $this->contact_last_name,
+            'contact_full_name' => $this->contact_full_name,
             'contact_email' => $this->contact_email,
             'contact_phone' => $this->contact_phone,
             'persons_count' => $this->whenCounted('persons'),

api/app/Http/Resources/Api/V1/MeResource.php

@@ -13,7 +13,9 @@ final class MeResource extends JsonResource
     {
         return [
             'id' => $this->id,
-            'name' => $this->name,
+            'first_name' => $this->first_name,
+            'last_name' => $this->last_name,
+            'full_name' => $this->full_name,
             'email' => $this->email,
             'timezone' => $this->timezone,
             'locale' => $this->locale,

api/app/Http/Resources/Api/V1/MemberResource.php

@@ -13,7 +13,9 @@ final class MemberResource extends JsonResource
     {
         return [
             'id' => $this->id,
-            'name' => $this->name,
+            'first_name' => $this->first_name,
+            'last_name' => $this->last_name,
+            'full_name' => $this->full_name,
             'email' => $this->email,
             'role' => $this->pivot?->role,
             'avatar' => $this->avatar,

api/app/Http/Resources/Api/V1/PersonResource.php

@@ -14,7 +14,9 @@ final class PersonResource extends JsonResource
         return [
             'id' => $this->id,
             'event_id' => $this->event_id,
-            'name' => $this->name,
+            'first_name' => $this->first_name,
+            'last_name' => $this->last_name,
+            'full_name' => $this->full_name,
             'email' => $this->email,
             'phone' => $this->phone,
             'status' => $this->status,
@@ -33,7 +35,9 @@ final class PersonResource extends JsonResource
                         'match_id' => $match->id,
                         'matched_user' => [
                             'id' => $match->matchedUser->id,
-                            'name' => $match->matchedUser->name,
+                            'first_name' => $match->matchedUser->first_name,
+                            'last_name' => $match->matchedUser->last_name,
+                            'full_name' => $match->matchedUser->full_name,
                             'email' => $match->matchedUser->email,
                         ],
                         'matched_on' => $match->matched_on->value,

api/app/Http/Resources/Api/V1/UserResource.php

@@ -13,7 +13,9 @@ final class UserResource extends JsonResource
     {
         return [
             'id' => $this->id,
-            'name' => $this->name,
+            'first_name' => $this->first_name,
+            'last_name' => $this->last_name,
+            'full_name' => $this->full_name,
             'email' => $this->email,
             'roles' => $this->getRoleNames()->values()->all(),
             'timezone' => $this->timezone,