✨ Add leader management functionality for Meetups

- ➕ Introduced `leaders`, `promoteLeader`, and `demoteLeader` methods in `Meetup` model for consistent handling of meetup leadership.
- ⚙️ Refactored `MeetupLeaderController` to use new leadership methods, improving reusability and maintainability.
- 👮‍♂️ Added `ValidNpub` validation rule for npub input standardization.
- 🧪 Added feature tests for leadership delegation and permissions.
- 🖼️ Implemented leader management UI in meetup edit page with flash messaging for actions.

tests/Feature/Meetups/ManageLeadersWebTest.php

@@ -0,0 +1,85 @@
+<?php
+
+use App\Models\City;
+use App\Models\Country;
+use App\Models\Meetup;
+use App\Models\User;
+use Livewire\Livewire;
+use swentel\nostr\Key\Key as NostrKey;
+
+beforeEach(function () {
+    $country = Country::factory()->create(['code' => 'de']);
+    $this->city = City::factory()->create(['country_id' => $country->id]);
+    $this->creator = actingAsUser();
+    $this->meetup = Meetup::factory()->create([
+        'city_id' => $this->city->id,
+        'created_by' => $this->creator->id,
+    ]);
+});
+
+function webNpub(string $hex): string
+{
+    return (new NostrKey)->convertPublicKeyToBech32($hex);
+}
+
+it('appoints a leader by npub from the edit page', function () {
+    $npub = webNpub(str_pad('a', 64, 'a'));
+
+    Livewire::test('meetups.edit', ['meetup' => $this->meetup])
+        ->set('leaderNpub', $npub)
+        ->call('addLeader')
+        ->assertHasNoErrors();
+
+    $newUser = User::where('nostr', $npub)->firstOrFail();
+
+    $this->assertDatabaseHas('meetup_user', [
+        'meetup_id' => $this->meetup->id,
+        'user_id' => $newUser->id,
+        'is_leader' => true,
+    ]);
+});
+
+it('rejects an invalid npub on the edit page', function () {
+    Livewire::test('meetups.edit', ['meetup' => $this->meetup])
+        ->set('leaderNpub', 'not-an-npub')
+        ->call('addLeader')
+        ->assertHasErrors('leaderNpub');
+});
+
+it('demotes a leader but keeps the membership', function () {
+    $leader = User::factory()->create();
+    $this->meetup->users()->syncWithoutDetaching([$leader->id => ['is_leader' => true]]);
+
+    Livewire::test('meetups.edit', ['meetup' => $this->meetup])
+        ->call('removeLeader', $leader->id)
+        ->assertHasNoErrors();
+
+    $this->assertDatabaseHas('meetup_user', [
+        'meetup_id' => $this->meetup->id,
+        'user_id' => $leader->id,
+        'is_leader' => false,
+    ]);
+});
+
+it('never lets the creator be demoted', function () {
+    Livewire::test('meetups.edit', ['meetup' => $this->meetup])
+        ->call('removeLeader', $this->creator->id)
+        ->assertStatus(403);
+
+    $this->assertDatabaseHas('meetup_user', [
+        'meetup_id' => $this->meetup->id,
+        'user_id' => $this->creator->id,
+        'is_leader' => true,
+    ]);
+});
+
+it('forbids a plain member from managing leaders via the edit page', function () {
+    $member = User::factory()->create();
+    $this->meetup->addMember($member); // is_leader = false
+
+    $this->actingAs($member);
+
+    // Nicht-Leader kommen schon nicht auf die Seite (authorizeAccess).
+    Livewire::test('meetups.edit', ['meetup' => $this->meetup])
+        ->assertStatus(403);
+});