Raise hero upload soft-warning from 1 MB to 5 MB

The "may slow the page" prompt is only a client-side nudge — the server
hard-limits uploads at 8 MB. 1 MB was arbitrarily low and nagged on
perfectly normal hero images. Bump to 5 MB (still well under the hard cap)
and pull the threshold + message into a single tooLargeToUpload() helper so
the background, moon, and image upload paths stay in sync.

client/src/routes/admin/views/HeroEditor.jsx

@@ -12,6 +12,17 @@ const round2 = (v) => Math.round(v * 100) / 100
 const genId = () => (crypto.randomUUID ? crypto.randomUUID() : `el-${Date.now()}-${Math.random()}`)
 const hexOf = (v) => (/^#([0-9a-f]{3}|[0-9a-f]{6})$/i.test(v || '') ? v : '#ffffff')
 
+// Soft page-weight warning shown before uploading a large hero image. This is
+// only a nudge (hero images render on the public landing page); the server hard-
+// limits uploads at 8 MB. Returns true when the caller should abort the upload.
+const WARN_UPLOAD_MB = 5
+function tooLargeToUpload(size) {
+  return (
+    size > WARN_UPLOAD_MB * 1024 * 1024 &&
+    !confirm(`This image is over ${WARN_UPLOAD_MB} MB and may slow the page. Upload anyway?`)
+  )
+}
+
 function newElement(type, z) {
   const base = { id: genId(), type, x: 50, y: 50, z, anchor: 'center' }
   if (type === 'text_block') {
@@ -206,7 +217,7 @@ export default function HeroEditor() {
     const file = e.target.files?.[0]
     e.target.value = ''
     if (!file) return
-    if (file.size > 1024 * 1024 && !confirm('This image is over 1 MB and may slow the page. Upload anyway?')) return
+    if (tooLargeToUpload(file.size)) return
     setUploading(true)
     try {
       const { url } = await api.admin.upload(file)
@@ -506,7 +517,7 @@ function MoonPanel({ element, onProps }) {
     const f = e.target.files?.[0]
     e.target.value = ''
     if (!f) return
-    if (f.size > 1024 * 1024 && !confirm('This image is over 1 MB and may slow the page. Upload anyway?')) return
+    if (tooLargeToUpload(f.size)) return
     setUp(true)
     try {
       const { url } = await api.admin.upload(f)
@@ -583,7 +594,7 @@ function ImagePanel({ element, onProps }) {
     const f = e.target.files?.[0]
     e.target.value = ''
     if (!f) return
-    if (f.size > 1024 * 1024 && !confirm('This image is over 1 MB and may slow the page. Upload anyway?')) return
+    if (tooLargeToUpload(f.size)) return
     setUp(true)
     try {
       const { url } = await api.admin.upload(f)