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-user/src/main/java/com/fruitshorts/user/dal/entity/AppAccountDeletion.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("app_account_deletion")
 public class AppAccountDeletion {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     /** pending/cancelled/completed */

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUser.java

@@ -16,7 +16,7 @@ import java.time.LocalDateTime;
 @TableName("app_user")
 public class AppUser {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     /** 对外用户标识，接口只暴露 uid，不暴露自增 ID */
     private String uid;

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserBanRecord.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("app_user_ban_record")
 public class AppUserBanRecord {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     /** BAN/LIMIT/MUTE */

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserConsent.java

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

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserCredential.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("app_user_credential")
 public class AppUserCredential {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private Long userId;
     /** PHONE/EMAIL/APPLE/GOOGLE */

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserDevice.java

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

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserOtp.java

@@ -15,7 +15,7 @@ import java.time.LocalDateTime;
 @TableName("app_user_otp")
 public class AppUserOtp {
 
-    @TableId(type = IdType.AUTO)
+    @TableId(type = IdType.ASSIGN_ID)
     private Long id;
     private String scene;
     private String targetType;

fruitshorts-module-user/src/main/java/com/fruitshorts/user/dal/entity/AppUserSession.java

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