feat(timetable): 13 form requests for artist domain endpoints

Created under app/Http/Requests/Api/V1/Artist/, mirroring the
existing FormRequest pattern (final class, authorize() returns true,
controller-level Gate::authorize). One request per CRUD shape plus the
two domain-specific endpoints:

  artists                     create / update
  genres                      create / update (with org-scoped unique)
  stages                      create / update (with event-scoped unique)
  stages/order                ReorderStagesRequest — permutation check
  engagements                 create / update — per RFC §10.3, with
                              ContractRequiresFee + OptionExpiresInFuture
                              conditional rules wired
  performances                create / update — per §10.2; cross-FK
                              engagement.event_id ↔ event_id chain
                              enforced via withValidator closure;
                              update is non-placement only (placement
                              edits go through /timetable/move)
  timetable/move              per §10.4; resolves target_event_id from
                              target_stage_id + target_start_at via
                              stage_days, then reuses StageActiveOnEvent
                              + WithinEventBounds for downstream rules
  stages/{stage}/days         §10.5 matrix replace; each event_id must
                              equal stage.event_id (flat) or be sub-event
                              (festival)

Custom error messages in Dutch where user-facing. Cross-FK rules that
span request inputs (engagement vs event-id chain, day matrix sub-event
membership) live in withValidator after-closures so the rule cache is
stable per request.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

api/app/Http/Requests/Api/V1/Artist/CreatePerformanceRequest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1\Artist;
+
+use App\Models\ArtistEngagement;
+use App\Models\Event;
+use App\Rules\Artist\StageActiveOnEvent;
+use App\Rules\Artist\WithinEventBounds;
+use Illuminate\Contracts\Validation\Validator;
+use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
+
+/**
+ * RFC v0.2 §10.2.
+ */
+final class CreatePerformanceRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function rules(): array
+    {
+        $event = $this->route('event');
+        $organisationId = $event instanceof Event ? $event->organisation_id : null;
+        $eventIdInput = (string) $this->input('event_id', '');
+
+        return [
+            'engagement_id' => [
+                'required', 'string', 'max:30',
+                Rule::exists('artist_engagements', 'id')->where('organisation_id', $organisationId),
+            ],
+            'event_id' => [
+                'required', 'string', 'max:30',
+                Rule::exists('events', 'id')->where('organisation_id', $organisationId),
+            ],
+            'stage_id' => [
+                'nullable', 'string', 'max:30',
+                Rule::exists('stages', 'id'),
+                new StageActiveOnEvent($eventIdInput),
+            ],
+            'start_at' => ['required', 'date_format:Y-m-d H:i:s', new WithinEventBounds($eventIdInput)],
+            'end_at' => ['required', 'date_format:Y-m-d H:i:s', 'after:start_at', new WithinEventBounds($eventIdInput)],
+            'lane' => ['nullable', 'integer', 'min:0', 'max:9'],
+            'notes' => ['nullable', 'string', 'max:1000'],
+        ];
+    }
+
+    public function withValidator(Validator $validator): void
+    {
+        $validator->after(function (Validator $validator): void {
+            $engagementId = $this->input('engagement_id');
+            $eventId = $this->input('event_id');
+            if (! is_string($engagementId) || ! is_string($eventId)) {
+                return;
+            }
+
+            $engagement = ArtistEngagement::query()->find($engagementId);
+            if ($engagement === null) {
+                return;
+            }
+
+            $event = Event::withoutGlobalScopes()->find($eventId);
+            if ($event === null) {
+                return;
+            }
+
+            // event_id must equal engagement.event_id (flat case) OR be a
+            // sub-event of engagement.event_id (festival case).
+            if (
+                $eventId !== $engagement->event_id
+                && $event->parent_event_id !== $engagement->event_id
+            ) {
+                $validator->errors()->add(
+                    'event_id',
+                    'event_id moet gelijk zijn aan de engagement.event_id of een sub-event daarvan.',
+                );
+            }
+        });
+    }
+}