feat(frontend): S1 回测核心页（新建/进度/结果 + ECharts 图表）

- api/strategy.ts、api/backtest.ts（含类型）
- 回测-新建（策略下拉+动态参数表单+日期+提交）
- useTask 组合式（轮询+WS 实时阶段）+ 进度页
- 结果页：统计全表 + 资金曲线 + 每日盈亏(红涨绿跌) + 成交表 + K线买卖点
- build 通过；result 接口扩 symbol/start/end 供 K线调用

frontend/src/composables/useTask.ts

@@ -0,0 +1,55 @@
+import { ref, onUnmounted } from 'vue'
+import { getStatus } from '@/api/backtest'
+import { useAuthStore } from '@/stores/auth'
+
+export type TaskState = 'pending' | 'running' | 'done' | 'failed' | 'unknown'
+
+/**
+ * Track a task's status + stage via polling (2s) and WebSocket (real-time).
+ * Auto-stops on unmount.
+ */
+export function useTask(taskId: string) {
+  const status = ref<TaskState>('unknown')
+  const stage = ref('')
+  let timer: ReturnType<typeof setInterval> | null = null
+  let ws: WebSocket | null = null
+
+  async function poll(): Promise<void> {
+    try {
+      const s = await getStatus(taskId)
+      status.value = s.status as TaskState
+      stage.value = s.stage
+    } catch {
+      /* transient — keep last known state */
+    }
+  }
+
+  function start(): void {
+    poll()
+    timer = setInterval(poll, 2000)
+    const proto = window.location.protocol === 'https:' ? 'wss' : 'ws'
+    const auth = useAuthStore()
+    const url = `${proto}://${window.location.host}/api/v1/ws/task/${taskId}?token=${auth.token}`
+    try {
+      ws = new WebSocket(url)
+      ws.onmessage = (ev) => {
+        try {
+          const msg = JSON.parse(ev.data)
+          if (msg.stage) stage.value = msg.stage
+          if (msg.status) status.value = msg.status
+        } catch {
+          /* ignore non-JSON keepalive frames */
+        }
+      }
+    } catch {
+      /* WS optional — polling covers it */
+    }
+  }
+
+  onUnmounted(() => {
+    if (timer) clearInterval(timer)
+    if (ws) ws.close()
+  })
+
+  return { status, stage, start }
+}