fix(data): enforce portfolio validation isolation

src/GmRelay.Bot/Migrations/V029__add_completed_game_portfolios_and_reviews.sql

@@ -67,6 +67,18 @@ BEGIN
         target_portfolio_game_id := OLD.portfolio_game_id;
     END IF;
 
+    IF current_setting('transaction_isolation') <> 'read committed'
+       AND EXISTS (
+           SELECT 1
+           FROM portfolio_games pg
+           WHERE pg.id = target_portfolio_game_id
+             AND pg.is_public = true
+       ) THEN
+        RAISE EXCEPTION
+            'portfolio publication validation requires read committed isolation'
+            USING ERRCODE = '0A000';
+    END IF;
+
     IF EXISTS (
         SELECT 1
         FROM portfolio_games pg