feat(engine): 新增 Python 策略引擎模块

- config/settings.py：Pydantic 解析 env.yaml
- data/db.py：asyncpg 连接池管理
- data/reader.py：KlineReader 只读查询 TimescaleDB
- data/models.py：KlineRecord 等 Pydantic 模型，镜像 TypeORM 实体
- example/test_db.py：数据库查询验证示例
- README.md：引擎架构文档

engine/data/db.py

@@ -0,0 +1,28 @@
+"""asyncpg 连接池管理 —— engine 模块对 TimescaleDB 的唯一切入点。"""
+
+import asyncpg
+from engine.config.settings import DB_DSN, db as db_config
+
+_pool: asyncpg.Pool | None = None
+
+
+async def get_pool() -> asyncpg.Pool:
+    """获取或创建 asyncpg 连接池（懒初始化，复用）。"""
+    global _pool
+    if _pool is None:
+        _pool = await asyncpg.create_pool(
+            dsn=DB_DSN,
+            min_size=2,
+            max_size=10,
+            command_timeout=30,
+            server_settings={"default_transaction_read_only": "on"},
+        )
+    return _pool
+
+
+async def close_pool() -> None:
+    """关闭连接池（应用退出时调用）"""
+    global _pool
+    if _pool:
+        await _pool.close()
+        _pool = None