fix(data): serialize portfolio publication validation

src/GmRelay.Bot/Migrations/V029__add_completed_game_portfolios_and_reviews.sql

@@ -59,6 +59,8 @@ AS $$
 DECLARE
     target_portfolio_game_id UUID;
 BEGIN
+    PERFORM pg_advisory_xact_lock(20260530, 108);
+
     IF TG_TABLE_NAME = 'portfolio_games' THEN
         target_portfolio_game_id := NEW.id;
     ELSE

src/GmRelay.DiscordBot/Features/Sessions/DiscordDeleteSessionHandler.cs

@@ -32,7 +32,9 @@ public sealed class DiscordDeleteSessionHandler(
               FROM group_managers gm
               JOIN players p ON p.id = gm.player_id
               JOIN game_groups g ON g.id = gm.group_id
-              WHERE g.platform = 'Discord' AND g.external_group_id = @GuildId",
+              WHERE g.platform = 'Discord'
+                AND p.platform = 'Discord'
+                AND g.external_group_id = @GuildId",
             new { GuildId = guildId });
 
         if (!permissionChecker.CanManageSchedule(guildOwnerId, userId, dbManagerUserIds, resolvedPermissions))