Add route-based code splitting and loading skeletons

- Lazy-load Dashboard, Comparison, Slides via React.lazy + Suspense
- Main bundle reduced from 606KB to 256KB
- Replace full-screen spinner with skeleton cards during load
- Skeleton used for both initial data fetch and route transitions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/App.css

@@ -1987,3 +1987,74 @@ html[dir="rtl"] .chart-export-btn.visible {
   direction: ltr !important;
   text-align: left !important;
 }
+
+/* ========================================
+   Loading Skeleton
+   ======================================== */
+
+@keyframes skeleton-pulse {
+  0%, 100% { opacity: 0.4; }
+  50% { opacity: 1; }
+}
+
+.skeleton-container {
+  padding: 80px 24px 24px;
+  max-width: 1200px;
+  margin: 0 auto;
+}
+
+.skeleton-stats {
+  display: grid;
+  grid-template-columns: repeat(4, 1fr);
+  gap: 16px;
+  margin-bottom: 24px;
+}
+
+.skeleton-card {
+  background: #f1f5f9;
+  border-radius: 12px;
+  padding: 20px;
+  animation: skeleton-pulse 1.5s ease-in-out infinite;
+}
+
+.skeleton-card-wide {
+  grid-column: span 2;
+}
+
+.skeleton-line {
+  background: #e2e8f0;
+  border-radius: 6px;
+}
+
+.skeleton-line-short {
+  width: 40%;
+  height: 14px;
+  margin-bottom: 12px;
+}
+
+.skeleton-line-tall {
+  width: 100%;
+  height: 120px;
+}
+
+.skeleton-card-wide .skeleton-line-tall {
+  height: 200px;
+}
+
+.skeleton-charts {
+  display: grid;
+  grid-template-columns: repeat(2, 1fr);
+  gap: 16px;
+}
+
+@media (max-width: 768px) {
+  .skeleton-stats {
+    grid-template-columns: repeat(2, 1fr);
+  }
+  .skeleton-charts {
+    grid-template-columns: 1fr;
+  }
+  .skeleton-card-wide {
+    grid-column: span 1;
+  }
+}

src/App.tsx

@@ -1,8 +1,10 @@
-import React, { useState, useEffect, useCallback, ReactNode } from 'react';
+import React, { useState, useEffect, useCallback, ReactNode, lazy, Suspense } from 'react';
 import { BrowserRouter as Router, Routes, Route, Link, useLocation } from 'react-router-dom';
-import Dashboard from './components/Dashboard';
-import Comparison from './components/Comparison';
-import Slides from './components/Slides';
+
+const Dashboard = lazy(() => import('./components/Dashboard'));
+const Comparison = lazy(() => import('./components/Comparison'));
+const Slides = lazy(() => import('./components/Slides'));
+import LoadingSkeleton from './components/shared/LoadingSkeleton';
 import { fetchData, getCacheStatus, refreshData } from './services/dataService';
 import { useLanguage } from './contexts/LanguageContext';
 import type { MuseumRecord, CacheStatus, DataErrorType } from './types';
@@ -83,9 +85,8 @@ function App() {
 
   if (loading) {
     return (
-      <div className="loading-container" dir={dir}>
-        <div className="loading-spinner"></div>
-        <p>{t('app.loading')}</p>
+      <div className="app" dir={dir}>
+        <LoadingSkeleton />
       </div>
     );
   }
@@ -191,11 +192,13 @@ function App() {
           </div>
         </nav>
         
-        <Routes>
-          <Route path="/" element={<Dashboard data={data} showDataLabels={showDataLabels} setShowDataLabels={setShowDataLabels} includeVAT={includeVAT} setIncludeVAT={setIncludeVAT} />} />
-          <Route path="/comparison" element={<Comparison data={data} showDataLabels={showDataLabels} setShowDataLabels={setShowDataLabels} includeVAT={includeVAT} setIncludeVAT={setIncludeVAT} />} />
-          <Route path="/slides" element={<Slides data={data} />} />
-        </Routes>
+        <Suspense fallback={<LoadingSkeleton />}>
+          <Routes>
+            <Route path="/" element={<Dashboard data={data} showDataLabels={showDataLabels} setShowDataLabels={setShowDataLabels} includeVAT={includeVAT} setIncludeVAT={setIncludeVAT} />} />
+            <Route path="/comparison" element={<Comparison data={data} showDataLabels={showDataLabels} setShowDataLabels={setShowDataLabels} includeVAT={includeVAT} setIncludeVAT={setIncludeVAT} />} />
+            <Route path="/slides" element={<Slides data={data} />} />
+          </Routes>
+        </Suspense>
         
         {/* Mobile Bottom Navigation */}
         <nav className="mobile-nav">

src/components/shared/LoadingSkeleton.tsx

@@ -0,0 +1,27 @@
+import React from 'react';
+
+function SkeletonCard({ wide = false }: { wide?: boolean }) {
+  return (
+    <div className={`skeleton-card ${wide ? 'skeleton-card-wide' : ''}`}>
+      <div className="skeleton-line skeleton-line-short" />
+      <div className="skeleton-line skeleton-line-tall" />
+    </div>
+  );
+}
+
+export default function LoadingSkeleton() {
+  return (
+    <div className="skeleton-container">
+      <div className="skeleton-stats">
+        <SkeletonCard />
+        <SkeletonCard />
+        <SkeletonCard />
+        <SkeletonCard />
+      </div>
+      <div className="skeleton-charts">
+        <SkeletonCard wide />
+        <SkeletonCard wide />
+      </div>
+    </div>
+  );
+}