fix: allow self-promotion to first admin in room

Users can now add themselves as the first admin without existing
admin permission. This enables /start in DMs to work correctly.

core/services.py

@@ -35,11 +35,15 @@ class BountyService:
     def add_admin(
         self, room_id: int, admin_user_id: int, requesting_user_id: int
     ) -> None:
-        """Add an admin to a room. Requires admin permission."""
+        """Add an admin to a room. Requires admin permission, or self-promotion if first admin."""
+        room_data = self._storage.load(room_id)
+        has_no_admins = room_data is None or not room_data.admin_user_ids
+        is_self_promotion = requesting_user_id == admin_user_id
+
         if not self.is_admin(room_id, requesting_user_id):
+            if not (has_no_admins and is_self_promotion):
                 raise PermissionError("Only admins can add admins.")
 
-        room_data = self._storage.load(room_id)
         if room_data is None:
             room_data = RoomData(
                 room_id=room_id, bounties=[], next_id=1, admin_user_ids=[]