修复(#85): 促销系统 quantity 设计修正补丁（跨任务统一修复）

- subscribe_promo 表加 quantity 字段，BIGINT NOT NULL DEFAULT 1
- EvaluatePromo 加 quantity 参数，按 subscribeID + quantity 精确匹配
- Promo 从 Subscribe 顶层移到 SubscribeDiscount
- 查询加 quantity，返回 map[subscribeID][quantity] 二级映射
- recordPromoUsage 错误向上传播，不再静默吞掉
- preCreate 和 purchase 的 allowPromo 判定统一为 orderType==1
- 迁移脚本增加幂等处理（guarded DROP/ADD/MODIFY）

Co-authored-by: multica-agent <github@multica.ai>

initialize/migrate/database/02154_promo_system.up.sql

@@ -14,19 +14,155 @@ CREATE TABLE IF NOT EXISTS `promo_rule` (
   KEY `idx_enabled_priority_deleted` (`enabled`, `deleted_at`, `priority` DESC)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='促销规则表';
 
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'promo_rule'
+    AND INDEX_NAME = 'idx_enabled_priority'
+);
+
+SET @sql = IF(
+  @index_exists = 1,
+  'ALTER TABLE `promo_rule` DROP INDEX `idx_enabled_priority`',
+  'SELECT ''Index idx_enabled_priority does not exist on promo_rule table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'promo_rule'
+    AND INDEX_NAME = 'idx_deleted_at'
+);
+
+SET @sql = IF(
+  @index_exists = 1,
+  'ALTER TABLE `promo_rule` DROP INDEX `idx_deleted_at`',
+  'SELECT ''Index idx_deleted_at does not exist on promo_rule table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'promo_rule'
+    AND INDEX_NAME = 'idx_enabled_priority_deleted'
+);
+
+SET @sql = IF(
+  @index_exists = 0,
+  'ALTER TABLE `promo_rule` ADD KEY `idx_enabled_priority_deleted` (`enabled`, `deleted_at`, `priority` DESC)',
+  'SELECT ''Index idx_enabled_priority_deleted already exists on promo_rule table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
 CREATE TABLE IF NOT EXISTS `subscribe_promo` (
   `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
   `subscribe_id` BIGINT UNSIGNED NOT NULL COMMENT '套餐规格 ID',
-  `quantity` INT NOT NULL DEFAULT 0 COMMENT '购买数量',
+  `quantity` BIGINT NOT NULL DEFAULT 1 COMMENT '购买数量',
   `promo_rule_id` BIGINT UNSIGNED NOT NULL COMMENT '促销规则 ID',
   `promo_price` BIGINT NOT NULL DEFAULT 0 COMMENT '该规格在此规则下的优惠价（分）',
   `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
   `updated_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
   PRIMARY KEY (`id`),
-  UNIQUE KEY `uk_subscribe_qty_rule` (`subscribe_id`, `quantity`, `promo_rule_id`),
+  UNIQUE KEY `uk_subscribe_quantity_rule` (`subscribe_id`, `quantity`, `promo_rule_id`),
   KEY `idx_promo_rule_id` (`promo_rule_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='规格促销价表';
 
+SET @column_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.COLUMNS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'subscribe_promo'
+    AND COLUMN_NAME = 'quantity'
+);
+
+SET @sql = IF(
+  @column_exists = 0,
+  'ALTER TABLE `subscribe_promo` ADD COLUMN `quantity` BIGINT NOT NULL DEFAULT 1 COMMENT ''购买数量'' AFTER `subscribe_id`',
+  'SELECT ''Column quantity already exists in subscribe_promo table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @sql = IF(
+  @column_exists = 1,
+  'ALTER TABLE `subscribe_promo` MODIFY COLUMN `quantity` BIGINT NOT NULL DEFAULT 1 COMMENT ''购买数量''',
+  'SELECT ''Column quantity does not exist in subscribe_promo table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'subscribe_promo'
+    AND INDEX_NAME = 'uk_subscribe_rule'
+);
+
+SET @sql = IF(
+  @index_exists = 1,
+  'ALTER TABLE `subscribe_promo` DROP INDEX `uk_subscribe_rule`',
+  'SELECT ''Index uk_subscribe_rule does not exist on subscribe_promo table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'subscribe_promo'
+    AND INDEX_NAME = 'uk_subscribe_qty_rule'
+);
+
+SET @sql = IF(
+  @index_exists = 1,
+  'ALTER TABLE `subscribe_promo` DROP INDEX `uk_subscribe_qty_rule`',
+  'SELECT ''Index uk_subscribe_qty_rule does not exist on subscribe_promo table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
+SET @index_exists = (
+  SELECT COUNT(*)
+  FROM INFORMATION_SCHEMA.STATISTICS
+  WHERE TABLE_SCHEMA = DATABASE()
+    AND TABLE_NAME = 'subscribe_promo'
+    AND INDEX_NAME = 'uk_subscribe_quantity_rule'
+);
+
+SET @sql = IF(
+  @index_exists = 0,
+  'ALTER TABLE `subscribe_promo` ADD UNIQUE KEY `uk_subscribe_quantity_rule` (`subscribe_id`, `quantity`, `promo_rule_id`)',
+  'SELECT ''Index uk_subscribe_quantity_rule already exists on subscribe_promo table'''
+);
+
+PREPARE stmt FROM @sql;
+EXECUTE stmt;
+DEALLOCATE PREPARE stmt;
+
 CREATE TABLE IF NOT EXISTS `promo_usage` (
   `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
   `user_id` BIGINT UNSIGNED NOT NULL COMMENT '用户 ID',