feat(orders): a fifth verdict, 'bad', between ok and never again

The jump from "OK" to "Never again" is too big and most
disappointments live in the gap (user, 2026-07-28) — so a merely poor
meal either flattered itself as OK or got blacklisted.

Only 'never' raises the warning on a future order. A blacklist that fires
for every mediocre delivery is one nobody reads, so 'bad' records the
disappointment without triggering the alarm. Both set order_again = false
— you would not choose either again — and that split between "would I
order it" and "warn me about it" is the point of the extra level.

Migration widens the CHECK; nothing is removed, so no existing row needs
mapping.

src/app/api/slack/interactive/route.ts

@@ -341,7 +341,8 @@ async function setRating(transactionId: number, participantId: number, rating: R
        SET rating = EXCLUDED.rating,
            order_again = EXCLUDED.order_again,
            updated_at = now()`,
-    [transactionId, participantId, rating, rating !== "never"]
+    // "bad" and "never" both mean no; only "never" warns on a future order.
+    [transactionId, participantId, rating, rating !== "never" && rating !== "bad"]
   );
 }