✨ 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.

resources/views/livewire/meetups/edit.blade.php

@@ -85,15 +85,13 @@ class extends Component {
     }
 
     /**
-     * Portal-Frontend nutzt die gelockerte updateViaPortal-Ability: Ersteller,
-     * Super-Admins UND Mitglieder der meetup_user-Pivot („Meine Meetups") dürfen
-     * die Stammdaten bearbeiten. REST-API und MCP-Tools bleiben auf der strikten
-     * update()-Ability (nur Ersteller/Super-Admin). Übergangslösung, bis ein
-     * echtes Rollen-/Freigabekonzept existiert.
+     * Stammdaten bearbeiten dürfen der Ersteller, Super-Admins UND delegierte
+     * Leader (meetup_user.is_leader). Einheitliche update-Ability für Portal-
+     * Frontend, REST-API und MCP-Tools (MeetupPolicy::update).
      */
     protected function authorizeAccess(): void
     {
-        if (auth()->guest() || auth()->user()->cannot('updateViaPortal', $this->meetup)) {
+        if (auth()->guest() || auth()->user()->cannot('update', $this->meetup)) {
             abort(403);
         }
     }