security: A01-13 — nest all event routes under organisation prefix

Move all authenticated organiser-facing event sub-resource routes from
/events/{event}/... to /organisations/{organisation}/events/{event}/...
to enforce multi-tenancy at the routing layer.

Changes:
- Routes: restructured api.php to nest all event sub-resources under
  the existing organisation prefix group
- Controllers: added Organisation parameter and VerifiesOrganisationEvent
  trait to all 12 affected controllers (sections, time-slots, shifts,
  persons, crowd-lists, locations, shift-assignments, registration-fields,
  availabilities, field-values, section-preferences, stats)
- Tests: updated all 20 feature test files with new route paths
- Frontend: updated 8 API composables and 20 Vue components/pages
- API.md: updated documentation to reflect new route structure

Portal routes, public routes (volunteer-register), and invitation routes
remain unchanged as they operate without organisation context.

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

api/app/Http/Controllers/Api/V1/RegistrationFormFieldController.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace App\Http\Controllers\Api\V1;
 
 use App\Http\Controllers\Controller;
+use App\Http\Controllers\Api\V1\Traits\VerifiesOrganisationEvent;
 use App\Http\Requests\Api\V1\ImportFromEventRequest;
 use App\Http\Requests\Api\V1\ReorderRegistrationFormFieldsRequest;
 use App\Http\Requests\Api\V1\StoreRegistrationFormFieldRequest;
@@ -23,13 +24,16 @@ use Illuminate\Support\Facades\Gate;
 
 final class RegistrationFormFieldController extends Controller
 {
+    use VerifiesOrganisationEvent;
+
     public function __construct(
         private readonly RegistrationFormFieldService $service,
         private readonly RegistrationFieldTemplateService $templateService,
     ) {}
 
-    public function index(Event $event): AnonymousResourceCollection
+    public function index(Organisation $organisation, Event $event): AnonymousResourceCollection
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('viewAny', [RegistrationFormField::class, $event]);
 
         $fields = $this->service->listForEvent($event);
@@ -37,8 +41,9 @@ final class RegistrationFormFieldController extends Controller
         return RegistrationFormFieldResource::collection($fields);
     }
 
-    public function store(StoreRegistrationFormFieldRequest $request, Event $event): JsonResponse
+    public function store(StoreRegistrationFormFieldRequest $request, Organisation $organisation, Event $event): JsonResponse
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('create', [RegistrationFormField::class, $event]);
 
         $field = $this->service->createField($event, $request->validated());
@@ -48,9 +53,11 @@ final class RegistrationFormFieldController extends Controller
 
     public function update(
         UpdateRegistrationFormFieldRequest $request,
+        Organisation $organisation,
         Event $event,
         RegistrationFormField $registrationField,
     ): JsonResponse {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('update', [$registrationField, $event]);
 
         $field = $this->service->updateField($registrationField, $request->validated());
@@ -58,8 +65,9 @@ final class RegistrationFormFieldController extends Controller
         return $this->success(new RegistrationFormFieldResource($field));
     }
 
-    public function destroy(Event $event, RegistrationFormField $registrationField): JsonResponse
+    public function destroy(Organisation $organisation, Event $event, RegistrationFormField $registrationField): JsonResponse
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('delete', [$registrationField, $event]);
 
         $this->service->deleteField($registrationField);
@@ -67,8 +75,9 @@ final class RegistrationFormFieldController extends Controller
         return response()->json(null, 204);
     }
 
-    public function reorder(ReorderRegistrationFormFieldsRequest $request, Event $event): JsonResponse
+    public function reorder(ReorderRegistrationFormFieldsRequest $request, Organisation $organisation, Event $event): JsonResponse
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('reorder', [RegistrationFormField::class, $event]);
 
         $this->service->reorderFields($event, $request->validated()['ids']);
@@ -76,8 +85,9 @@ final class RegistrationFormFieldController extends Controller
         return response()->json(null, 204);
     }
 
-    public function fromTemplate(Request $request, Event $event): JsonResponse
+    public function fromTemplate(Request $request, Organisation $organisation, Event $event): JsonResponse
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('create', [RegistrationFormField::class, $event]);
 
         $request->validate([
@@ -95,8 +105,9 @@ final class RegistrationFormFieldController extends Controller
         return $this->created(new RegistrationFormFieldResource($field));
     }
 
-    public function importFromEvent(ImportFromEventRequest $request, Event $event): JsonResponse
+    public function importFromEvent(ImportFromEventRequest $request, Organisation $organisation, Event $event): JsonResponse
     {
+        $this->verifyEventBelongsToOrganisation($organisation, $event);
         Gate::authorize('create', [RegistrationFormField::class, $event]);
 
         $sourceEvent = Event::findOrFail($request->validated()['source_event_id']);