feat: scroll-to-top button in estore; fix JS/CSS cache headers on main site

- Add ScrollToTop component matching main site's green Top button
  (appears after 130px scroll, same styling and font)
- Fix main-site server.js: JS/CSS now use max-age=3600 + must-revalidate
  instead of 30d immutable — changes reach users within 1 hour instead
  of being stuck in browser cache for a month
- Images/fonts keep 30d immutable (safe, as they are content-addressed)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

estore/src/app/layout.tsx

@@ -5,6 +5,7 @@ import Footer from '@/components/Footer'
 import CartDrawer from '@/components/CartDrawer'
 import CartFab from '@/components/CartFab'
 import { CartProvider } from '@/context/CartContext'
+import ScrollToTop from '@/components/ScrollToTop'
 
 export const metadata: Metadata = {
   title: {
@@ -51,6 +52,7 @@ export default function RootLayout({ children }: { children: React.ReactNode })
           <CartFab />
           <main>{children}</main>
           <Footer />
+          <ScrollToTop />
         </CartProvider>
       </body>
     </html>

estore/src/components/ScrollToTop.tsx

@@ -0,0 +1,45 @@
+'use client'
+
+import { useEffect, useState } from 'react'
+
+export default function ScrollToTop() {
+  const [visible, setVisible] = useState(false)
+
+  useEffect(() => {
+    const onScroll = () => {
+      const scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop || 0
+      setVisible(scrollTop > 130)
+    }
+    window.addEventListener('scroll', onScroll, { passive: true })
+    return () => window.removeEventListener('scroll', onScroll)
+  }, [])
+
+  if (!visible) return null
+
+  return (
+    <button
+      aria-label="Back to top"
+      onClick={() => window.scrollTo({ top: 0, left: 0, behavior: 'smooth' })}
+      style={{
+        position:        'fixed',
+        bottom:          '12px',
+        right:           '10px',
+        zIndex:          99,
+        border:          '1px solid #363636',
+        outline:         'none',
+        background:      '#94d601',
+        cursor:          'pointer',
+        padding:         '15px',
+        borderRadius:    '10px',
+        fontSize:        '18px',
+        boxShadow:       '3px 3px 3px #363636',
+        fontFamily:      '"Autour One", serif',
+        lineHeight:      1,
+      }}
+      onMouseEnter={(e) => { (e.currentTarget as HTMLButtonElement).style.background = '#aedad3' }}
+      onMouseLeave={(e) => { (e.currentTarget as HTMLButtonElement).style.background = '#94d601' }}
+    >
+      Top
+    </button>
+  )
+}

main-site/server.js

@@ -64,8 +64,13 @@ const staticCacheOptions = {
     maxAge: process.env.NODE_ENV === 'production' ? '30d' : 0,
     setHeaders: (res, filePath) => {
         if (filePath.endsWith('.html') || filePath.endsWith('update.json')) {
+            // Never cache HTML or live data
             res.setHeader('Cache-Control', 'no-store');
-        } else if (/\.(js|css|svg|ico|png|jpg|jpeg|webp|avif|woff2?)$/i.test(filePath)) {
+        } else if (/\.(js|css)$/i.test(filePath)) {
+            // JS/CSS: 1 hour, must revalidate — allows updates to reach users quickly
+            res.setHeader('Cache-Control', 'public, max-age=3600, must-revalidate');
+        } else if (/\.(png|jpg|jpeg|webp|avif|svg|ico|woff2?)$/i.test(filePath)) {
+            // Images/fonts: 30 days immutable (these are named by content, rarely change)
             res.setHeader('Cache-Control', 'public, max-age=2592000, immutable');
         }
     }