fix(tournament): remove matches for participants before deletion

- Added logic to delete all matches associated with a participant before their removal from the tournament, ensuring data integrity and preventing orphaned match records.

backend/services/tournamentService.js

@@ -3380,6 +3380,16 @@ Ve    // 2. Neues Turnier anlegen
         if (!participant) {
             throw new Error('Externer Teilnehmer nicht gefunden');
         }
+        // Lösche alle Matches, in denen dieser Teilnehmer spielt
+        await TournamentMatch.destroy({
+            where: {
+                tournamentId,
+                [Op.or]: [
+                    { player1Id: participantId },
+                    { player2Id: participantId }
+                ]
+            }
+        });
         await participant.destroy();
     }