feat: #27 插件系统 — 第三方节点扩展

- NodePlugin 模型: manifest规范（name/version/node_type/inputs_schema/outputs_schema）
- plugin_loader 服务: manifest校验、代码加载/卸载、沙箱执行（subprocess隔离+超时30s）
- plugins API: CRUD、启用/禁用、市场浏览、安装计数、沙箱测试执行
- PluginMarket.vue: 插件市场上传/浏览/安装/启用禁用/删除/测试
- 注册 register_external_tool 到 tool_registry，供工作流编辑器使用

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

backend/app/main.py

@@ -263,7 +263,7 @@ async def startup_event():
         logger.error(f"人参果1号长连接启动失败: {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, approval
+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, orchestration_templates, plugins
 
 app.include_router(auth.router)
 app.include_router(uploads.router)
@@ -292,6 +292,8 @@ app.include_router(agent_schedules.router)
 app.include_router(notifications.router)
 app.include_router(feishu_bind.router)
 app.include_router(approval.router)
+app.include_router(plugins.router)
+app.include_router(orchestration_templates.router)
 
 if __name__ == "__main__":
     import uvicorn