feat(db): P1 Alembic+模型整合 — 唯一总库基线迁移 + 培训/园区 ORM 模型

- 新增 alembic（ini/env async/script.mako/versions/0001_initial）。
- models.py 并入培训表(training_accounts/events/bookings/tests/courses/policy/plan/survey_logs)
  与园区表(park_tenants/companies/kb_docs/screens)，与平台同库、命名加域前缀避免撞名。
- baseline 迁移用 create_all(幂等)：既有平台表保留，新增培训/园区表被建。
- 验证：对临时库 uv run alembic upgrade head 建出全部新表。

alembic/env.py

@@ -0,0 +1,63 @@
+# -*- coding: utf-8 -*-
+"""Alembic 迁移环境（async engine，target_metadata=Base.metadata）。
+
+数据库 URL 取服务端配置 config.DATABASE_URL（同应用唯一总库），
+迁移/建表均通过 alembic 运行，不在应用启动时执行。
+"""
+from __future__ import annotations
+
+import asyncio
+import os
+import sys
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy import pool
+from sqlalchemy.ext.asyncio import async_engine_from_config
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from app import config as app_config
+from app.infrastructure.db import Base
+import app.infrastructure.models  # noqa: F401 确保模型注册到 Base.metadata
+
+config = context.config
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# 用应用统一 DATABASE_URL（可被 env PINEAGENTS_DEMO_DATABASE_URL 覆盖）
+config.set_main_option("sqlalchemy.url", app_config.DATABASE_URL)
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    context.configure(url=app_config.DATABASE_URL, target_metadata=target_metadata,
+                      literal_binds=True, dialect_opts={"paramstyle": "named"})
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection) -> None:
+    context.configure(connection=connection, target_metadata=target_metadata)
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    connectable = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.", poolclass=pool.NullPool,
+    )
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+    await connectable.dispose()
+
+
+def run_migrations_online() -> None:
+    asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()