feat: 可配置方案引擎通用原型（Mock 检索）

需求未定稿时可先跑通追问/判定/出方案；槽位与判定树外置 YAML，后续可接 Ragflow。

Co-authored-by: haijd <haijd@163.com>

engine/app/settings.py

@@ -0,0 +1,22 @@
+from pathlib import Path
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+ROOT = Path(__file__).resolve().parents[2]
+KNOWLEDGE_DIR = ROOT / "knowledge"
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    app_name: str = "鲜境方案引擎原型"
+    knowledge_dir: Path = KNOWLEDGE_DIR
+    retrieval_backend: str = "mock"  # mock | ragflow
+    ragflow_base_url: str = "http://127.0.0.1:9380"
+    ragflow_api_key: str = ""
+    ragflow_dataset_ids: str = ""
+    llm_mode: str = "template"  # template（无 Key 可跑）| openai_compatible（预留）
+
+
+settings = Settings()