perf: avoid blocking page render on data refresh

src/components/Layout.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useCallback, useState, useEffect } from 'react';
 import { Outlet, Link, useLocation } from 'react-router-dom';
 import { LayoutDashboard, Users, BarChart3, ChevronLeft, ChevronRight, Package, Loader2, LogOut, Megaphone } from 'lucide-react';
 import type { DateRange, OrderData, StockData } from '../types';
@@ -32,19 +32,22 @@ const Layout = () => {
     return saved ? Number(saved) : 0;
   });
 
-  const loadData = async (showLoading = false) => {
+  const loadData = useCallback(async (showLoading = false) => {
     if (showLoading) setIsLoading(true);
-    const [data, stock] = await Promise.all([fetchData(), fetchStock()]);
-    setOrdersData(data);
-    setStockData(stock);
-    if (showLoading) setIsLoading(false);
-  };
+    try {
+      const [data, stock] = await Promise.all([fetchData(), fetchStock()]);
+      setOrdersData(data);
+      setStockData(stock);
+    } finally {
+      if (showLoading) setIsLoading(false);
+    }
+  }, []);
 
   useEffect(() => {
-    // The dashboard has to fetch its initial server state after mount.
+    // The dashboard fetches its initial server state after mount without blocking route render.
     // eslint-disable-next-line react-hooks/set-state-in-effect
-    void loadData(true);
-  }, []);
+    void loadData(false).finally(() => setIsLoading(false));
+  }, [loadData]);
 
   useEffect(() => {
     if (refreshInterval === 0) return;
@@ -54,7 +57,7 @@ const Layout = () => {
     }, refreshInterval);
 
     return () => clearInterval(intervalId);
-  }, [refreshInterval]);
+  }, [loadData, refreshInterval]);
 
   useEffect(() => {
     localStorage.setItem('nexstar_refresh_interval', refreshInterval.toString());
@@ -146,13 +149,13 @@ const Layout = () => {
 
         {/* Content Area */}
         <div className="flex-1 overflow-y-auto p-8 relative">
-          {isLoading ? (
-             <div className="flex items-center justify-center h-full">
-                <Loader2 className="w-8 h-8 text-brand-primary animate-spin" />
-             </div>
-          ) : (
-             <Outlet context={{ dateRange, setDateRange, ordersData, stockData, refreshInterval, setRefreshInterval, loadData }} />
+          {isLoading && (
+            <div className="absolute right-8 top-8 z-10 flex items-center gap-2 rounded-xl border border-dark-border bg-dark-card px-3 py-2 text-sm font-semibold text-dark-muted shadow-sm">
+              <Loader2 className="h-4 w-4 animate-spin text-brand-primary" />
+              Atualizando dados
+            </div>
           )}
+          <Outlet context={{ dateRange, setDateRange, ordersData, stockData, isDataLoading: isLoading, refreshInterval, setRefreshInterval, loadData }} />
         </div>
       </main>
     </div>

src/pages/ClientDetails.tsx

@@ -17,6 +17,14 @@ const ClientDetails = () => {
     return new Intl.NumberFormat('pt-BR', { style: 'currency', currency: 'BRL' }).format(value);
   };
 
+  if (!groupedOrders.length && ordersData.length === 0) {
+    return (
+      <div className="text-center py-12">
+        <p className="text-zinc-500 dark:text-dark-muted font-medium">Carregando cliente...</p>
+      </div>
+    );
+  }
+
   if (!groupedOrders.length) {
     return (
       <div className="text-center py-12">

src/pages/ProductDetails.tsx

@@ -43,6 +43,14 @@ const ProductDetails = () => {
     return new Intl.NumberFormat('pt-BR', { style: 'currency', currency: 'BRL' }).format(value);
   };
 
+  if (!productInfo && ordersData.length === 0) {
+    return (
+      <div className="text-center py-12">
+        <p className="text-zinc-500 dark:text-dark-muted font-medium">Carregando produto...</p>
+      </div>
+    );
+  }
+
   if (!productInfo) {
     return (
       <div className="text-center py-12">