feat: add stickers delete api

internal/repository/sadhna_reward_repo.go

@@ -206,6 +206,29 @@ func (r *RewardRepo) CreateCustom(ctx context.Context, key, name, meaning, image
 	return &w, nil
 }
 
+// DeleteCustom removes an admin-made reward from the catalog.
+//
+// Both sadhna_reward_grants.reward_id and saved_stickers.reward_id are
+// ON DELETE CASCADE, so this also takes it out of every devotee's gallery and
+// sticker vault. Stickers already SENT in a chat are unaffected: those copy
+// the artwork onto the message rather than referencing the catalog, so history
+// stays intact.
+//
+// Restricted to custom keys. A seeded reward would come straight back on the
+// next Seed run, and deleting one would rip a streak reward out of the
+// galleries of everyone who earned it.
+func (r *RewardRepo) DeleteCustom(ctx context.Context, key string) error {
+	tag, err := r.pg.Pool.Exec(ctx,
+		`DELETE FROM sadhna_rewards WHERE key = $1 AND key LIKE 'custom\_%'`, key)
+	if err != nil {
+		return fmt.Errorf("delete custom reward: %w", err)
+	}
+	if tag.RowsAffected() == 0 {
+		return ErrRewardNotFound
+	}
+	return nil
+}
+
 // ByKey looks up one reward from the catalog.
 func (r *RewardRepo) ByKey(ctx context.Context, key string) (*model.SadhnaReward, error) {
 	var w model.SadhnaReward