fix(tournament): update birth year eligibility checks in TournamentTab

- Adjusted the logic for member eligibility based on birth year to ensure that members without a valid birth date are not allowed in age-restricted classes.
- Enhanced comments for clarity regarding age restrictions and eligibility criteria, improving the understanding of the filtering logic.

frontend/src/views/TournamentTab.vue

@@ -1667,9 +1667,15 @@ export default {
                 if (classItem.gender === 'male' && g !== 'male') return false;
                 if (classItem.gender === 'female' && g !== 'female') return false;
             }
-            // Geburtsjahr-Filter
+            
+            // Wenn Klasse keine Geburtsjahr-Einschränkung hat, alle erlauben
+            const hasAgeRestriction = classItem.minBirthYear != null || classItem.maxBirthYear != null;
+            if (!hasAgeRestriction) return true;
+            
+            // Geburtsjahr-Filter: Bei Altersklassen MUSS ein gültiges Geburtsjahr vorhanden sein
             const bd = member.birthDate;
-            if (!bd) return true; // Kein Geburtsdatum = erlaubt
+            if (!bd) return false; // Kein Geburtsdatum = NICHT erlaubt bei Altersklassen
+            
             let birthYear = null;
             if (typeof bd === 'string' && bd.includes('-')) {
                 birthYear = parseInt(bd.split('-')[0], 10);
@@ -1677,20 +1683,9 @@ export default {
                 const parts = bd.split('.');
                 if (parts.length >= 3) birthYear = parseInt(parts[2], 10);
             }
-            if (birthYear == null || !Number.isFinite(birthYear)) return true;
             
-            // Debug: Zeige Filterung für erste paar Mitglieder
-            if (Math.random() < 0.1) {
-                console.log('[memberEligibleForClass]', {
-                    member: `${member.firstName} ${member.lastName}`,
-                    birthYear,
-                    classItem: classItem.name,
-                    minBirthYear: classItem.minBirthYear,
-                    maxBirthYear: classItem.maxBirthYear,
-                    tooOld: classItem.minBirthYear != null && birthYear < classItem.minBirthYear,
-                    tooYoung: classItem.maxBirthYear != null && birthYear > classItem.maxBirthYear
-                });
-            }
+            // Kein gültiges Geburtsjahr parsbar = nicht erlaubt bei Altersklassen
+            if (birthYear == null || !Number.isFinite(birthYear)) return false;
             
             if (classItem.minBirthYear != null && birthYear < classItem.minBirthYear) return false;
             if (classItem.maxBirthYear != null && birthYear > classItem.maxBirthYear) return false;