feat: add 灵犀 Feishu bot + fix agent schedule system + default all tools

- Add 灵犀学习助手 Feishu bot (lingxi_app_service + lingxi_ws_handler)
- Fix agent_schedule_service missing AgentSchedule import (Celery Beat)
- Fix scene_templates default enable_tools=False → True
- Fix workflow_engine LLM node: empty tools list now = all tools (consistent with agent node)
- Add 创建agent.md guide document

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/core/config.py

@@ -105,6 +105,11 @@ class Settings(BaseSettings):
     TIANTIAN_APP_SECRET: str = ""
     TIANTIAN_AGENT_ID: str = ""  # 创建苏瑶3号后写入
 
+    # 灵犀飞书应用配置（独立 WS 连接，路由到灵犀学习助手 Agent）
+    LINGXI_APP_ID: str = ""
+    LINGXI_APP_SECRET: str = ""
+    LINGXI_AGENT_ID: str = ""  # 创建灵犀后写入
+
     class Config:
         env_file = str(_ENV_PATH)
         case_sensitive = True