✨ Add addToMine functionality to Meetups API for adding meetups to a user's "My Meetups" list

- 🔒 Introduce `addToMine` policy for authenticated users to add existing meetups.
- ✏️ Add `addToMine` method in `MeetupController` with idempotent handling.
- ✨ Include `addMember` utility in `Meetup` model for managing pivot relationships.
- 🛠️ Refactor `AddMeetupToMineTool` to use `addMember` for consistency.
- 🧪 Add feature tests for `addToMine`, covering idempotency, permissions, and unknown slugs.
- 🌐 Register `addToMine` route in API and link it to `MeetupController`.

app/Mcp/Tools/Meetup/AddMeetupToMineTool.php

@@ -39,17 +39,13 @@ class AddMeetupToMineTool extends Tool
             }
         }
 
-        $alreadyMember = $meetup->users()->whereKey($user->getAuthIdentifier())->exists();
-
-        $meetup->users()->syncWithoutDetaching([
-            $user->getAuthIdentifier() => ['is_leader' => false],
-        ]);
+        $wasAdded = $meetup->addMember($user);
 
         return Response::json([
             'meetup' => MeetupResource::make($meetup)->resolve(),
-            'message' => $alreadyMember
-                ? '„'.$meetup->name.'" war bereits Teil deiner Meetups.'
-                : '„'.$meetup->name.'" wurde zu deinen Meetups hinzugefügt.',
+            'message' => $wasAdded
+                ? '„'.$meetup->name.'" wurde zu deinen Meetups hinzugefügt.'
+                : '„'.$meetup->name.'" war bereits Teil deiner Meetups.',
         ]);
     }