✨ 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/dashboard.blade.php

@@ -179,15 +179,20 @@ class extends Component {
                                     </a>
                                 </div>
                                 <div class="flex flex-row items-center gap-2 w-full sm:w-auto">
-                                    <flux:button
-                                        :href="route_with_country('meetups.events.create', ['meetup' => $meetup])"
-                                        variant="primary" icon="calendar" size="xs">
-                                        {{ __('Neues Event erstellen') }}
-                                    </flux:button>
-                                    <flux:button :href="route_with_country('meetups.edit', ['meetup' => $meetup])"
-                                                 size="xs" variant="ghost" icon="pencil" class="w-full sm:w-auto">
-                                        {{ __('Bearbeiten') }}
-                                    </flux:button>
+                                    {{-- Termine & Stammdaten nur für Leader dieses Meetups
+                                         (meetup_user.is_leader); Mitglieder ohne Leaderschaft
+                                         können das Meetup nur aus „Meine“ entfernen. --}}
+                                    @if($meetup->pivot->is_leader)
+                                        <flux:button
+                                            :href="route_with_country('meetups.events.create', ['meetup' => $meetup])"
+                                            variant="primary" icon="calendar" size="xs">
+                                            {{ __('Neues Event erstellen') }}
+                                        </flux:button>
+                                        <flux:button :href="route_with_country('meetups.edit', ['meetup' => $meetup])"
+                                                     size="xs" variant="ghost" icon="pencil" class="w-full sm:w-auto">
+                                            {{ __('Bearbeiten') }}
+                                        </flux:button>
+                                    @endif
                                     <flux:modal.trigger :name="'remove-meetup-' . $meetup->id">
                                         <flux:button class="cursor-pointer" size="xs" variant="danger"
                                                      icon="trash"></flux:button>