✨ Implement leadership-based permissions for Meetup management

- 🔒 Restrict event creation, editing, and deletion to Meetup leaders (`is_leader`) and creators for consistency across APIs, frontend, and MCP.
- ➕ Add new APIs for leader delegation: assign/remove Meetup leaders via `meetup_user.is_leader`.
- 🛠️ Replace loose member checks with specific leadership checks in policies, controllers, and views.
- 🧪 Add exhaustive tests to ensure only eligible leaders execute critical actions (e.g., event creation/edit, Meetup updates).
- 🔄 Refactor pivot relationships and models (`leadByMe`, `isLeader`) for explicit leadership handling.
- ✨ Introduce artisan command `meetups:promote-existing-leaders` to transition legacy data.

app/Http/Requests/Api/StoreMeetupEventRequest.php

@@ -3,15 +3,23 @@
 namespace App\Http\Requests\Api;
 
 use App\Enums\RecurrenceType;
-use App\Models\MeetupEvent;
+use App\Models\Meetup;
 use Illuminate\Foundation\Http\FormRequest;
 use Illuminate\Validation\Rule;
 
 class StoreMeetupEventRequest extends FormRequest
 {
+    /**
+     * Termine darf nur anlegen, wer das zugehörige Meetup bearbeiten darf
+     * (Ersteller/Leader/Super-Admin) — dieselbe Berechtigung wie die
+     * Stammdaten. Existenz/Pflicht von meetup_id prüft rules() (422); ist ein
+     * gültiges Meetup angegeben, muss der Nutzer dafür berechtigt sein.
+     */
     public function authorize(): bool
     {
-        return $this->user()->can('create', MeetupEvent::class);
+        $meetup = Meetup::find($this->input('meetup_id'));
+
+        return $meetup === null || $this->user()->can('update', $meetup);
     }
 
     /**