chore(backend): 引入 sqlite-vec 依赖并配置数据目录

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

backend/app/config.py

@@ -1,25 +1,40 @@
 import os
 from dataclasses import dataclass
 from functools import lru_cache
+from pathlib import Path
+
+# backend 目录（本文件位于 backend/app/config.py，父目录的父目录即 backend）
+BACKEND_DIR = Path(__file__).resolve().parent.parent
 
 
 @dataclass(frozen=True)
 class Settings:
-    """应用基础配置；正式环境可通过 APP_* 环境变量覆盖。"""
+    """应用基础配置；正式环境可通过 APP_* 环境变量覆盖。
+
+    数据目录默认落在 backend/data 下：app.db 保存 SQLite 索引，
+    vault/ 保存 Markdown 笔记。三者均可通过环境变量覆盖，便于测试与正式部署分离。
+    """
 
     name: str
     version: str
     environment: str
     host: str
     port: int
+    data_dir: Path
+    db_path: Path
+    vault_path: Path
 
 
 @lru_cache
 def get_settings() -> Settings:
+    data_dir = Path(os.getenv("APP_DATA_DIR", str(BACKEND_DIR / "data")))
     return Settings(
         name=os.getenv("APP_NAME", "Notes Agent AI Core"),
         version=os.getenv("APP_VERSION", "0.1.0"),
         environment=os.getenv("APP_ENVIRONMENT", "development"),
         host=os.getenv("APP_HOST", "127.0.0.1"),
         port=int(os.getenv("APP_PORT", "8000")),
+        data_dir=data_dir,
+        db_path=Path(os.getenv("APP_DB_PATH", str(data_dir / "app.db"))),
+        vault_path=Path(os.getenv("APP_VAULT_PATH", str(data_dir / "vault"))),
     )