revert(db): remove Alembic migration system

Remove Alembic database migration system in favor of delta scripts:

Deleted:
- runtime/datamate-python/alembic.ini (config file)
- runtime/datamate-python/alembic/env.py (environment config)
- runtime/datamate-python/alembic/script.py.mako (migration template)
- runtime/datamate-python/alembic/versions/20250205_0001_add_file_version.py (migration)

Modified:
- scripts/db/data-annotation-init.sql
  - Removed alembic_version table creation and version insertion
  - Kept file_version column in t_dm_annotation_results

Rationale:
- Alembic migration testing failed in production
- Delta scripts are simpler and more reliable for this project
- SQL init scripts contain complete schema including latest changes

scripts/db/data-annotation-init.sql

@@ -1467,22 +1467,6 @@ INSERT INTO t_dm_annotation_templates (
     '1.0.0'
 );
 
--- =============================================
--- Alembic 版本控制表（标记数据库已应用最新迁移）
--- 说明：如果使用此脚本初始化数据库，则不需要再运行 Alembic 升级
--- =============================================
-
--- 创建 alembic_version 表（如果不存在）
-CREATE TABLE IF NOT EXISTS alembic_version (
-    version_num VARCHAR(32) NOT NULL PRIMARY KEY
-) COMMENT='Alembic 迁移版本记录表';
-
--- 清除现有版本记录（避免重复插入错误）
-DELETE FROM alembic_version;
-
--- 插入当前最新版本（与 alembic/versions/20250205_0001_add_file_version.py 对应）
-INSERT INTO alembic_version (version_num) VALUES ('20250205_0001');
-
 -- =============================================
 -- 完成提示
 -- =============================================