AppDbContext: Use records instead of unnamed tuples for buckets

Elwig/Documents/DeliveryConfirmation.cs

@@ -10,7 +10,7 @@ namespace Elwig.Documents {
         public Season Season;
         public DeliveryConfirmationData Data;
         public string? Text = App.Client.TextDeliveryConfirmation;
-        public Dictionary<string, (string, int, int, int, int)> MemberBuckets;
+        public Dictionary<string, MemberBucket> MemberBuckets;
 
         public DeliveryConfirmation(AppDbContext ctx, int year, Member m, DeliveryConfirmationData data) :
             base($"Anlieferungsbestätigung {year}", m) {