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/UpdateGenreRequest.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Requests\Api\V1\Artist;
+
+use App\Models\Genre;
+use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
+
+final class UpdateGenreRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function rules(): array
+    {
+        $genre = $this->route('genre');
+        $organisationId = $genre instanceof Genre
+            ? $genre->organisation_id
+            : ($this->route('organisation')?->id ?? null);
+        $genreId = $genre instanceof Genre ? $genre->id : null;
+
+        return [
+            'name' => [
+                'sometimes', 'required', 'string', 'max:40',
+                Rule::unique('genres', 'name')
+                    ->where('organisation_id', $organisationId)
+                    ->ignore($genreId),
+            ],
+            'color' => ['sometimes', 'nullable', 'string', 'size:7', 'regex:/^#[0-9A-Fa-f]{6}$/'],
+            'sort_order' => ['sometimes', 'nullable', 'integer', 'min:0'],
+            'is_active' => ['sometimes', 'boolean'],
+        ];
+    }
+}