feat: Phase 2 - Orchestrator workflow node + tool-level human approval

2.1 Orchestrator in workflow:
- New run_orchestrator_node() in workflow_integration.py loads agents from DB,
  supports route/sequential/debate/pipeline modes
- New 'orchestrator' node type in workflow_engine.py execute_node dispatch

2.2 Tool-level human approval:
- AgentToolConfig extended with require_approval, approval_timeout_ms,
  approval_default fields
- New ApprovalManager (approval_manager.py) with asyncio.Event-based
  create/wait_for_decision/resolve pattern
- AgentRuntime run() and run_stream() intercept tool execution,
  wait for approval decision before executing
- New POST /api/v1/approval/{id}/resolve REST endpoint
- Frontend: approval_required SSE event handling, approval dialog UI
  with approve/deny/skip buttons

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

backend/app/main.py

@@ -249,7 +249,7 @@ async def startup_event():
         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
+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, approval
 
 app.include_router(auth.router)
 app.include_router(uploads.router)
@@ -277,6 +277,7 @@ app.include_router(knowledge_base.router)
 app.include_router(agent_schedules.router)
 app.include_router(notifications.router)
 app.include_router(feishu_bind.router)
+app.include_router(approval.router)
 
 if __name__ == "__main__":
     import uvicorn