✨ Add RSVP functionality for Meetup Events

- 🏷️ Introduce `RsvpStatus` enum for managing attendance states (`attending`, `maybe`, `none`).
- ✏️ Add `MeetupEventController` methods for RSVP actions (`rsvpStatus`, `rsvp`) and payload handling.
- ✨ Implement RSVP helpers in `MeetupEvent` model for user-specific attendance management.
- 🌐 Register RSVP routes for showing and updating attendance in the API.
- 🧪 Add feature tests for RSVP actions, covering validation, idempotency, and correct list handling.

tests/Feature/Api/MeetupEventRsvpApiTest.php

@@ -0,0 +1,84 @@
+<?php
+
+use App\Models\MeetupEvent;
+use App\Models\User;
+use Laravel\Sanctum\Sanctum;
+
+it('rejects a guest', function () {
+    $event = MeetupEvent::factory()->create();
+
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'attending'])
+        ->assertUnauthorized();
+});
+
+it('lets an authenticated user attend', function () {
+    Sanctum::actingAs($user = User::factory()->create(['name' => 'Satoshi']));
+    $event = MeetupEvent::factory()->create();
+
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'attending'])
+        ->assertSuccessful()
+        ->assertJson(['status' => 'attending', 'attendees' => 1, 'might_attendees' => 0]);
+
+    expect($event->fresh()->attendees)->toBe(["id_{$user->id}|Satoshi"]);
+});
+
+it('moves the user between lists without duplicating', function () {
+    Sanctum::actingAs($user = User::factory()->create(['name' => 'Satoshi']));
+    $event = MeetupEvent::factory()->create();
+
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'attending']);
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'maybe'])
+        ->assertJson(['status' => 'maybe', 'attendees' => 0, 'might_attendees' => 1]);
+
+    $event->refresh();
+    expect($event->attendees)->toBe([])
+        ->and($event->might_attendees)->toBe(["id_{$user->id}|Satoshi"]);
+});
+
+it('withdraws the user with status none', function () {
+    Sanctum::actingAs($user = User::factory()->create(['name' => 'Satoshi']));
+    $event = MeetupEvent::factory()->create();
+
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'attending']);
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'none'])
+        ->assertJson(['status' => 'none', 'attendees' => 0, 'might_attendees' => 0]);
+
+    expect($event->fresh()->attendees)->toBe([]);
+});
+
+it('keeps other attendees untouched', function () {
+    $event = MeetupEvent::factory()->create([
+        'attendees' => ['id_999|Hal', 'id_50|Nick'],
+    ]);
+    Sanctum::actingAs($user = User::factory()->create(['name' => 'Satoshi']));
+
+    // id_5 darf id_50 nicht versehentlich treffen (Prefix-Abgrenzung per Pipe).
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'attending'])
+        ->assertJson(['attendees' => 3]);
+
+    expect($event->fresh()->attendees)
+        ->toContain('id_999|Hal')
+        ->toContain('id_50|Nick')
+        ->toContain("id_{$user->id}|Satoshi");
+});
+
+it('reports the current status and counts', function () {
+    Sanctum::actingAs($user = User::factory()->create(['name' => 'Satoshi']));
+    $event = MeetupEvent::factory()->create([
+        'attendees' => ['id_999|Hal'],
+        'might_attendees' => ["id_{$user->id}|Satoshi"],
+    ]);
+
+    $this->getJson("/api/meetup-events/{$event->id}/rsvp")
+        ->assertSuccessful()
+        ->assertJson(['status' => 'maybe', 'attendees' => 1, 'might_attendees' => 1]);
+});
+
+it('validates the status value', function () {
+    Sanctum::actingAs(User::factory()->create());
+    $event = MeetupEvent::factory()->create();
+
+    $this->postJson("/api/meetup-events/{$event->id}/rsvp", ['status' => 'bogus'])
+        ->assertUnprocessable()
+        ->assertJsonValidationErrors(['status']);
+});