feat(backend): 搭建 FastAPI 分层骨架 — 配置加载 / 健康检查 / SQLAlchemy+Alembic 就位

- uv 工程（Python 3.12，pyproject + uv.lock，dev: pytest/ruff）
- 分层包结构：api / application / domain / infrastructure / quant(qlib_adapter) / agent / core
- app.core.config：加载根 config.yaml + .env，sqlite 相对路径解析到项目根 data/
- SQLAlchemy Base + Session 工厂（Infrastructure 层，业务走 Repository）
- Alembic 迁移环境就位（env.py 复用应用配置，render_as_batch 兼容 SQLite）
- GET /api/health + pytest 冒烟 6 项通过 / ruff clean / uvicorn 启动验证

backend/app/infrastructure/persistence/migrations/env.py

@@ -0,0 +1,64 @@
+"""Alembic 迁移环境：从应用配置读取 DATABASE_URL 并连接 Base.metadata。
+
+用法（cd backend）：
+    uv run alembic revision --autogenerate -m "add xxx table"
+    uv run alembic upgrade head
+"""
+
+from __future__ import annotations
+
+from logging.config import fileConfig
+
+from alembic import context
+from app.core.config import get_settings
+from app.infrastructure.persistence.sqlalchemy.base import Base
+from sqlalchemy import engine_from_config, pool
+
+config = context.config
+
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+config.set_main_option("sqlalchemy.url", get_settings().database_url)
+
+target_metadata = Base.metadata
+
+
+def run_migrations_offline() -> None:
+    """离线模式：只生成 SQL，不连接数据库。"""
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+        render_as_batch=True,  # SQLite 支持 ALTER 需要 batch 模式
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """在线模式：连接数据库执行迁移。"""
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection,
+            target_metadata=target_metadata,
+            render_as_batch=True,
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()