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/main.py

@@ -241,6 +241,13 @@ async def startup_event():
     except Exception as e:
         logger.error(f"甜甜长连接启动失败: {e}")
 
+    # 启动灵犀飞书长连接（学习助手）
+    try:
+        from app.services.lingxi_ws_handler import start_ws_client as start_lingxi_ws
+        asyncio.ensure_future(start_lingxi_ws())
+    except Exception as e:
+        logger.error(f"灵犀长连接启动失败: {e}")
+
 # 注册路由
 from app.api import auth, uploads, workflows, executions, websocket, execution_logs, data_sources, agents, platform_templates, model_configs, webhooks, template_market, batch_operations, collaboration, permissions, monitoring, alert_rules, node_test, node_templates, tools, agent_chat, agent_monitoring, knowledge_base, agent_schedules, notifications, feishu_bind