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/core/config.py

@@ -0,0 +1,126 @@
+"""核心配置层：加载根目录 config.yaml + .env，向全应用提供 Settings。
+
+加载优先级：环境变量 > 根目录 .env > 根目录 config.yaml > 代码默认值。
+密钥只存在于 .env（config.yaml 经 *_env 字段引用变量名）。
+"""
+
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from functools import lru_cache
+from pathlib import Path
+
+import yaml
+
+# 项目根：<root>/backend/app/core/config.py → parents[3]
+PROJECT_ROOT = Path(__file__).resolve().parents[3]
+BACKEND_ROOT = PROJECT_ROOT / "backend"
+CONFIG_PATH = PROJECT_ROOT / "config.yaml"
+ENV_PATH = PROJECT_ROOT / ".env"
+
+_SQLITE_PREFIX = "sqlite:///"
+
+
+def _load_env_file(path: Path) -> None:
+    """把 .env 读入 os.environ（不覆盖已存在的环境变量）。"""
+    if not path.exists():
+        return
+    for raw in path.read_text(encoding="utf-8").splitlines():
+        line = raw.strip()
+        if not line or line.startswith("#") or "=" not in line:
+            continue
+        key, _, value = line.partition("=")
+        key = key.strip()
+        if key and key not in os.environ:
+            os.environ[key] = value.strip().strip("\"'")
+
+
+def _load_config_yaml(path: Path) -> dict:
+    if not path.exists():
+        return {}
+    with path.open(encoding="utf-8") as fh:
+        data = yaml.safe_load(fh)
+    return data if isinstance(data, dict) else {}
+
+
+def _deep(cfg: dict, dotted: str) -> object:
+    node: object = cfg
+    for part in dotted.split("."):
+        if not isinstance(node, dict) or part not in node:
+            return None
+        node = node[part]
+    return node
+
+
+@dataclass(frozen=True)
+class Settings:
+    """应用全局配置（已解析、不可变）。"""
+
+    app_name: str
+    app_version: str
+    debug: bool
+    secret_key: str
+    api_prefix: str
+    database_url: str
+    sqlalchemy_echo: bool
+    migrations_dir: Path
+    data_source_primary: str
+    data_source_fallback: str
+    tushare_token: str
+    storage: dict[str, Path]
+    config_path: Path = CONFIG_PATH
+    env_path: Path = ENV_PATH
+    project_root: Path = PROJECT_ROOT
+
+
+def _resolve_storage_dirs(cfg: dict) -> dict[str, Path]:
+    storage_cfg = _deep(cfg, "storage") or {}
+    return {
+        key: PROJECT_ROOT / str(value)
+        for key, value in storage_cfg.items()
+        if isinstance(value, str)
+    }
+
+
+def _normalize_sqlite_url(url: str) -> str:
+    """把相对路径的 sqlite URL 解析为项目根下的绝对路径。"""
+    if not url.startswith(_SQLITE_PREFIX):
+        return url
+    rest = url[len(_SQLITE_PREFIX) :]
+    if rest.startswith("/"):  # 已是绝对路径（sqlite:////abs/path）
+        return url
+    return f"{_SQLITE_PREFIX}{(PROJECT_ROOT / rest).resolve()}"
+
+
+@lru_cache
+def get_settings() -> Settings:
+    """加载并缓存 Settings。config / env 路径可通过参数覆盖以便测试。"""
+    _load_env_file(ENV_PATH)
+    cfg = _load_config_yaml(CONFIG_PATH)
+
+    secret_env = _deep(cfg, "app.secret_key_env") or "APP_SECRET_KEY"
+    url_env = _deep(cfg, "database.url_env") or "DATABASE_URL"
+    token_env = _deep(cfg, "data_source.tushare_token_env") or "TUSHARE_TOKEN"
+
+    default_url = "sqlite:///./data/quant.db"
+    database_url = os.environ.get(url_env) or default_url
+
+    migrations_rel = _deep(cfg, "database.migrations_dir") or (
+        "app/infrastructure/persistence/migrations"
+    )
+
+    return Settings(
+        app_name=str(_deep(cfg, "app.name") or "qlib-platform"),
+        app_version=str(_deep(cfg, "app.version") or "0.1.0"),
+        debug=bool(_deep(cfg, "app.debug") or False),
+        secret_key=os.environ.get(secret_env, "dev-insecure-key"),
+        api_prefix=str(_deep(cfg, "api.prefix") or "/api"),
+        database_url=_normalize_sqlite_url(database_url),
+        sqlalchemy_echo=bool(_deep(cfg, "database.echo") or False),
+        migrations_dir=BACKEND_ROOT / str(migrations_rel),
+        data_source_primary=str(_deep(cfg, "data_source.primary") or "tushare"),
+        data_source_fallback=str(_deep(cfg, "data_source.fallback") or "sina"),
+        tushare_token=os.environ.get(token_env, ""),
+        storage=_resolve_storage_dirs(cfg),
+    )