feat: add backend API for flexible account record upload and validation, including concurrent account_id fetching, and a new frontend upload page.

frontend/src/pages/Upload.tsx

@@ -58,6 +58,7 @@ export default function Upload() {
   const [status, setStatus] = useState<ProcessStatus | null>(null)
   const [polling, setPolling] = useState(false)
   const [loading, setLoading] = useState(false)
+  const [refreshing, setRefreshing] = useState(false)
   const [importResult, setImportResult] = useState<{
     imported: number
     total: number
@@ -232,8 +233,13 @@ export default function Upload() {
           <Button
             variant="outline"
             size="sm"
-            onClick={() => { loadStats(); fetchStatus(); }}
-            icon={<RefreshCw className={`h-4 w-4 ${polling ? 'animate-spin' : ''}`} />}
+            disabled={refreshing}
+            onClick={async () => {
+              setRefreshing(true)
+              await Promise.all([loadStats(), fetchStatus()])
+              setTimeout(() => setRefreshing(false), 500)
+            }}
+            icon={<RefreshCw className={`h-4 w-4 ${refreshing || polling ? 'animate-spin' : ''}`} />}
           >
             刷新
           </Button>