feat: schema v1.7 + sections/shifts frontend

- Universeel festival/event model (parent_event_id, event_type)
- event_person_activations pivot tabel
- Event model: parent/children relaties + helper scopes
- DevSeeder: festival structuur met sub-events
- Sections & Shifts frontend (twee-kolom layout)
- BACKLOG.md aangemaakt met 22 gedocumenteerde wensen

api/database/migrations/2026_04_08_400000_add_festival_columns_to_events_table.php

@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('events', function (Blueprint $table) {
+            $table->foreignUlid('parent_event_id')
+                ->nullable()
+                ->after('organisation_id')
+                ->constrained('events')
+                ->nullOnDelete();
+
+            $table->enum('event_type', ['event', 'festival', 'series'])
+                ->default('event')
+                ->after('status');
+
+            $table->string('event_type_label')
+                ->nullable()
+                ->after('event_type');
+
+            $table->string('sub_event_label')
+                ->nullable()
+                ->after('event_type_label');
+
+            $table->boolean('is_recurring')
+                ->default(false)
+                ->after('sub_event_label');
+
+            $table->string('recurrence_rule')
+                ->nullable()
+                ->after('is_recurring');
+
+            $table->json('recurrence_exceptions')
+                ->nullable()
+                ->after('recurrence_rule');
+
+            $table->index('parent_event_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('events', function (Blueprint $table) {
+            $table->dropForeign(['parent_event_id']);
+            $table->dropIndex(['parent_event_id']);
+            $table->dropColumn([
+                'parent_event_id',
+                'event_type',
+                'event_type_label',
+                'sub_event_label',
+                'is_recurring',
+                'recurrence_rule',
+                'recurrence_exceptions',
+            ]);
+        });
+    }
+};

api/database/migrations/2026_04_08_410000_create_event_person_activations_table.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('event_person_activations', function (Blueprint $table) {
+            $table->id();
+            $table->foreignUlid('event_id')->constrained('events')->cascadeOnDelete();
+            $table->foreignUlid('person_id')->constrained('persons')->cascadeOnDelete();
+
+            $table->unique(['event_id', 'person_id']);
+            $table->index('person_id');
+            $table->index('event_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('event_person_activations');
+    }
+};