added export tests feature

frontend/src/api.js

@@ -39,6 +39,20 @@ export const api = {
     return request('GET', `/schedule/week?${params.toString()}`)
   },
   getRerunTests: () => request('GET', '/tests/rerun'),
+
+  exportWindow: async (windowId) => {
+    const params = new URLSearchParams({ window_id: windowId })
+    const res = await fetch(`${BASE}/schedule/export?${params}`)
+    if (!res.ok) {
+      const err = await res.json().catch(() => ({ detail: res.statusText }))
+      throw new Error(err.detail || `HTTP ${res.status}`)
+    }
+    const blob = await res.blob()
+    const disposition = res.headers.get('Content-Disposition') ?? ''
+    const match = disposition.match(/filename="([^"]+)"/)
+    const filename = match ? match[1] : 'tests.zip'
+    return { blob, filename }
+  },
 }
 
 // Transform the flat items array from GET /api/schedule/week into the