feat(deploy): 完成数据迁移与MySQL全链路(14表698k消息100%一致+5方言补丁+bind mount)

- migrate_sqlite_to_mysql.py: 逐表清空重导(幂等),复用repos强转,JSON列
  解析,67万消息按msg_id键集分批,467s跑完14表全一致
- 修4个MySQL实测bug: NULLS LAST语法(compat.py编译补丁)、message.text
  TEXT→MEDIUMTEXT(64KB字节上限,实测20.8万字符车源清单)、URL列
  String(1024)→Text(分享链接超1KB)、垃圾超长member_id源头清理
- compose: media改bind mount(不占C盘Docker虚拟磁盘,实测2.5GB卷把
  C盘撑爆引擎500);mysql不映射宿主机3306
- 前端Dockerfile: npm ci→install(本地/容器npm版本锁漂移)
- 五服务实测:nginx→backend→MySQL全链路返回真实数据(客户6859/A**杰25条
  /搜索56条),媒体49536文件bind mount直读

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

yunke-server/app/db/base.py

@@ -15,6 +15,7 @@ from sqlalchemy.ext.asyncio import (
 from sqlalchemy.orm import DeclarativeBase
 
 from app.config import get_settings
+from app.db import compat  # noqa: F401,I100 — 注册 MySQL NULLS LAST 编译补丁(导入即生效)
 
 
 class Base(DeclarativeBase):