feat: fix time slot hierarchy — seeder, API include_children, frontend dropdown, navigation

Restructure the festival hierarchy end-to-end:

Seeder: Remove duplicate festival-level VOLUNTEER time slots, keep only CREW
operational slots. Rename sub-events to "Dag 1/2/3 — ..." pattern. Change
Nachtsecurity to Security (cross_event). EHBO/Security shifts now use sub-event
time slots via cross_event exception. Add flat event "Braderie Dorpstown 2026".

API: Add ?include_children=true to TimeSlotController for festivals, returning
all sub-event time slots with source and event_name fields. Update
StoreShiftRequest and UpdateShiftRequest to accept child time slots for
cross_event sections.

Frontend: Create useTimeSlotDropdown composable with 4-scenario dropdown logic.
Replace AppSelect with VAutocomplete in CreateShiftDialog with grouped items,
dimmed festival slots, and info tooltips. Add InfoTooltip reusable component.
Show festival context labels on cross_event sections in sub-event section lists.
Add read-only festival time slots on sub-event time-slots page. Add cross_event
context banner with "Bekijk alle diensten" link.

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

api/app/Http/Requests/Api/V1/UpdateShiftRequest.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace App\Http\Requests\Api\V1;
 
+use App\Models\Event;
 use Illuminate\Foundation\Http\FormRequest;
 use Illuminate\Validation\Rule;
 
@@ -20,12 +21,21 @@ final class UpdateShiftRequest extends FormRequest
         return [
             'time_slot_id' => ['sometimes', 'ulid', Rule::exists('time_slots', 'id')->where(function ($query) {
                 $event = $this->route('event');
+                $section = $this->route('section');
                 $eventIds = [$event->id];
 
+                // Sub-event: also accept parent festival time slots
                 if ($event->isSubEvent() && $event->parent_event_id) {
                     $eventIds[] = $event->parent_event_id;
                 }
 
+                // Cross_event section: also accept all sub-event time slots
+                if ($section && $section->type === 'cross_event') {
+                    $childIds = Event::where('parent_event_id', $event->id)
+                        ->pluck('id')->toArray();
+                    $eventIds = array_merge($eventIds, $childIds);
+                }
+
                 $query->whereIn('event_id', $eventIds);
             })],
             'location_id' => ['nullable', 'ulid', Rule::exists('locations', 'id')->where('event_id', $this->route('event')->id)],