feat(timetable): add 5 artist-domain policies

ArtistPolicy, ArtistEngagementPolicy, StagePolicy, PerformancePolicy,
GenrePolicy. Role-based authorization mirroring PersonPolicy/ShiftPolicy
pattern: super_admin bypass, org-membership check via wherePivotIn,
event_manager fallback for event-level operations.

Each policy carries a class-level docblock mapping the RFC §9
permission strings (events.view_program, events.manage_program,
organisations.manage_artists, organisations.manage_settings) to the
roles authorised, deferring permission-based authorisation to
AUTH-PERMISSIONS-MIGRATION.

ArtistPolicy.delete additionally guards on no-active-engagements
(D27): blocks soft-delete while any engagement is not Cancelled,
Rejected, or Declined.

PerformancePolicy.move and StagePolicy.reorder reuse canManageProgram
so the move endpoint and stage-reorder share the manage_program
permission semantics.

Auto-discovered by Laravel 11 (policies live at App\Policies\* matching
top-level App\Models\* — no explicit Gate::policy registration needed).

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

api/app/Policies/ArtistPolicy.php

@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Policies;
+
+use App\Enums\Artist\ArtistEngagementStatus;
+use App\Models\Artist;
+use App\Models\Organisation;
+use App\Models\User;
+
+/**
+ * Authorization model — role-based per existing codebase pattern.
+ *
+ * RFC v0.2 §9 permission mapping (deferred to AUTH-PERMISSIONS-MIGRATION
+ * when fine-grained permissions are operationally required):
+ *   organisations.manage_artists — program_manager, org_admin, super_admin
+ *   (read-only access — any authenticated organisation member)
+ */
+final class ArtistPolicy
+{
+    public function viewAny(User $user, Organisation $organisation): bool
+    {
+        return $user->hasRole('super_admin')
+            || $organisation->users()->where('user_id', $user->id)->exists();
+    }
+
+    public function view(User $user, Artist $artist): bool
+    {
+        return $user->hasRole('super_admin')
+            || $artist->organisation->users()->where('user_id', $user->id)->exists();
+    }
+
+    public function create(User $user, Organisation $organisation): bool
+    {
+        return $this->canManageArtists($user, $organisation);
+    }
+
+    public function update(User $user, Artist $artist): bool
+    {
+        return $this->canManageArtists($user, $artist->organisation);
+    }
+
+    /**
+     * Soft-delete is blocked while the artist still has any non-terminal
+     * engagement (D27 — soft-delete preserves historical engagements but
+     * the master must not vanish underneath an active booking).
+     */
+    public function delete(User $user, Artist $artist): bool
+    {
+        if (! $this->canManageArtists($user, $artist->organisation)) {
+            return false;
+        }
+
+        $hasActive = $artist->engagements()
+            ->whereNotIn('booking_status', [
+                ArtistEngagementStatus::Cancelled->value,
+                ArtistEngagementStatus::Rejected->value,
+                ArtistEngagementStatus::Declined->value,
+            ])
+            ->exists();
+
+        return ! $hasActive;
+    }
+
+    public function restore(User $user, Artist $artist): bool
+    {
+        return $this->canManageArtists($user, $artist->organisation);
+    }
+
+    private function canManageArtists(User $user, Organisation $organisation): bool
+    {
+        if ($user->hasRole('super_admin')) {
+            return true;
+        }
+
+        return $organisation->users()
+            ->where('user_id', $user->id)
+            ->wherePivotIn('role', ['org_admin', 'program_manager'])
+            ->exists();
+    }
+}