refactor: remove forum and topic feature chains

tools/adr-classes-domain-placement.md

@@ -19,7 +19,6 @@ Domain folders were frozen after the root→domain move. Theme types then migrat
 | User center/home/badges/level/metrics/notifications/follow | `User` | Account surface |
 | Credits, balance wallet, signin, invite, points-free | `Credits` | Points + cash wallet |
 | Download tokens/state, content pay, VIP, visibility | `Content` | Post-centric paid content |
-| Topic pay, plate follow pay | `Forum` | Forum SKUs (not generic content pay) |
 | Orders, gateways, coupon, charge-card, revenue, creator-revenue, withdrawal, rebate, discount, after-sale, shipping, wechat-notify | `Payment` | Commerce + settlement |
 | Shop services/meta/reviews | `Shop` | Product catalog / cart |
 | SMS stack | `Sms` | Messaging channel |