feat(portfolio): strategy 字段全链透传(API→orchestrator→worker→runner_backtest + 前端选择器)

后端: PortfolioBacktestRequest.strategy → submit_portfolio(strategy=) → spec →
portfolio_worker _build_argv --strategy(NAS local + Mac SSH 两分支)
前端: PortfolioBacktestReq.strategy? + 策略下拉(4选项) + 副标题动态 + onSubmit 透传
runner_backtest CLI 已支持 --strategy(choices 4 策略),本提交不动

frontend/src/api/portfolio.ts

@@ -2,6 +2,7 @@ import { apiClient } from './client'
 
 export interface PortfolioBacktestReq {
   pool: string
+  strategy?: string
   start_date: string
   end_date: string
   initial_cash: number