feat(tournament): add cleanup logic for orphaned matches

- Implemented a new method to clean up orphaned matches where at least one player no longer exists, enhancing data integrity in tournament management.
- Added a corresponding route and frontend functionality to trigger the cleanup process, allowing users to easily remove invalid match records.
- Updated localization strings to support the new feature, ensuring clarity in the user interface.

backend/services/tournamentService.js

@@ -3201,6 +3201,38 @@ Ve    // 2. Neues Turnier anlegen
         await TournamentMatch.destroy({ where });
     }
 
+    /**
+     * Entfernt Matches, bei denen mindestens ein Spieler nicht mehr existiert
+     * (z.B. gelöscht bevor die Aufräum-Logik beim Teilnehmerlöschen eingeführt wurde).
+     */
+    async cleanupOrphanedMatches(userToken, clubId, tournamentId) {
+        await checkAccess(userToken, clubId);
+        const tournament = await Tournament.findByPk(tournamentId);
+        if (!tournament || tournament.clubId != clubId) {
+            throw new Error('Turnier nicht gefunden');
+        }
+
+        const members = await TournamentMember.findAll({ where: { tournamentId }, attributes: ['id'] });
+        const externals = await ExternalTournamentParticipant.findAll({ where: { tournamentId }, attributes: ['id'] });
+        const validIds = new Set([
+            ...members.map(m => m.id),
+            ...externals.map(e => e.id)
+        ]);
+
+        const matches = await TournamentMatch.findAll({ where: { tournamentId } });
+        let deletedCount = 0;
+        for (const m of matches) {
+            const p1Exists = !m.player1Id || validIds.has(m.player1Id);
+            const p2Exists = !m.player2Id || validIds.has(m.player2Id);
+            if (!p1Exists || !p2Exists) {
+                await TournamentResult.destroy({ where: { matchId: m.id } });
+                await m.destroy();
+                deletedCount++;
+            }
+        }
+        return { deletedCount };
+    }
+
     async removeParticipant(userToken, clubId, tournamentId, participantId) {
         await checkAccess(userToken, clubId);