feat: S0 主键改雪花（DDL 去 identity + 实体 ASSIGN_ID + 雪花配置）

为什么：自增主键把 ID 分配锁在单库序列上，分库分表时无法横向扩展。趁线上业务数据
近零（只有系统种子表有量）先改，代价最低。

- sql/schema.sql、sql/schema-phase1.sql、sql/partition-maintenance.sql：61 处
  GENERATED BY DEFAULT AS IDENTITY 去掉，主键改 BIGINT 无默认值
- 52 个实体 @TableId IdType.AUTO -> IdType.ASSIGN_ID；两个入口 id-type: assign_id，
  并加 global-config.sequence.worker-id/datacenter-id（单机固定值，多实例需按实例分配）
- 新增 sql/migrate-s0-snowflake.sql：存量库幂等迁移，走 DROP IDENTITY 保留数据，不重建表
- 实测：三份建表脚本在新库连跑两遍幂等；线上 57 张表 identity 归零；
  watch_history/playback_ticket/order_event 的主键与唯一索引仍含分区键

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/CoinLedger.java

@@ -12,7 +12,7 @@ import java.time.LocalDateTime;
 @TableName("coin_ledger")
 public class CoinLedger {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     /** 正数入账、负数出账 */

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/Entitlement.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("entitlement")
 public class Entitlement {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     private Long dramaId;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/OrderEvent.java

@@ -12,7 +12,7 @@ import java.time.LocalDateTime;
 @TableName("order_event")
 public class OrderEvent {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private String orderNo;
     private String event;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/Orders.java

@@ -16,7 +16,7 @@ import java.time.LocalDateTime;
 @TableName("orders")
 public class Orders {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private String orderNo;
     private Long userId;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/Product.java

@@ -16,7 +16,7 @@ import java.time.LocalDateTime;
 @TableName("product")
 public class Product {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private String code;
     private String name;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/ReconcileTask.java

@@ -14,7 +14,7 @@ import java.time.LocalDateTime;
 @TableName("reconcile_task")
 public class ReconcileTask {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private LocalDate bizDate;
     private String platform;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/StoreReceipt.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("store_receipt")
 public class StoreReceipt {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private String platform;
     private String transactionId;

fruitshorts-module-commerce/src/main/java/com/fruitshorts/commerce/dal/entity/Wallet.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("wallet")
 public class Wallet {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     private Long coinBalance;