fix(db): 修复 seed 中文乱码

mysql 命令加 --default-character-set=utf8mb4，
SQL 文件头加 SET NAMES utf8mb4

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/dev.sh

@@ -60,7 +60,7 @@ cmd_seed() {
   fi
 
   info "写入 ${shop} 种子数据 → 容器 ${container} / ${db_name}"
-  docker exec -i "$container" mysql -uroot -p"$db_pass" "$db_name" < "$sql_file"
+  docker exec -i "$container" mysql --default-character-set=utf8mb4 -uroot -p"$db_pass" "$db_name" < "$sql_file"
   success "✅ ${shop} 种子数据写入完成"
   echo ""
   echo "  登录信息:"