feat: Enhance user group management and transaction handling in stored procedures

- Improved user group deletion logic to accurately report success or failure.
- Updated user group renaming checks to prevent unintended inserts or updates.
- Added documentation on transaction blocking risks during full resets in stored procedures.
- Removed unnecessary login scripts from database project.

Fuchs_Database/dbo/Stored Procedures/fis_admin_delUserGroup.sql

@@ -13,6 +13,11 @@ BEGIN
 	SET NOCOUNT ON;
 	DECLARE @utcnow datetime = GETUTCDATE();
 	DECLARE @auth smallint = [dbo].[fis_admin_getUserAuth](@authaccount);
+	-- Tracks whether THIS call actually soft-deleted an active group, so a never-existing or
+	-- already-deleted @usergroup_id reports failure instead of a false "ok:true" (the previous
+	-- version derived success from "not currently active", which is also true when nothing here
+	-- ever existed).
+	DECLARE @deleted bit = 0;
 
     IF @auth > 1 AND EXISTS (SELECT * FROM [dbo].[fis_usergroups] WHERE [usergroup_id] = @usergroup_id and [DateDeleted] is null)
 		BEGIN
@@ -21,10 +26,22 @@ BEGIN
 				SET [UserDeleted] = @authaccount
 				   ,[DateDeleted] = @utcnow
 			 WHERE
-				  [usergroup_id] = @usergroup_id;
+				  [usergroup_id] = @usergroup_id
+				  AND [DateDeleted] is null;
+
+			IF @@ROWCOUNT > 0 SET @deleted = 1;
+
+			-- Soft-delete the group's active memberships too, matching the confirm text
+			-- ("Die Mitgliedschaft aller Benutzer in dieser Gruppe geht dabei verloren.").
+			UPDATE [dbo].[fis_usergroups_members]
+				SET [UserDeleted] = @authaccount
+				   ,[DateDeleted] = @utcnow
+			 WHERE
+				  [usergroup_id] = @usergroup_id
+				  AND [DateDeleted] is null;
 
 		END
 
-	SELECT CAST((CASE WHEN NOT EXISTS (SELECT * FROM [dbo].[fis_usergroups] WHERE [usergroup_id] = @usergroup_id and [DateDeleted] is null) THEN 1 ELSE 0 END) as bit);
+	SELECT @deleted;
 
 END