chore: clean up sitemap and remove 0-byte placeholder files

- Remove testflight from sitemap (page is noindex, shouldn't be sitemapped)
- Use static lastModified dates instead of new Date() (prevents unnecessary
  sitemap churn on every deploy; new Date() changes the sitemap on every build)
- Delete public/header.png and public/news-welcome.png (0-byte placeholders
  no longer referenced anywhere; all feeds now use icon-1024.png)

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

Author: JoeMatt

public/header.png

@@ -4,15 +4,13 @@ export const dynamic = 'force-static'
 
 export default function sitemap(): MetadataRoute.Sitemap {
   const base = 'https://icube-emu.com'
-  const now = new Date()
   return [
-    { url: `${base}/`,            lastModified: now, changeFrequency: 'weekly',  priority: 1.0 },
-    { url: `${base}/downloads/`,  lastModified: now, changeFrequency: 'weekly',  priority: 0.9 },
-    { url: `${base}/testflight/`, lastModified: now, changeFrequency: 'weekly',  priority: 0.8 },
-    { url: `${base}/features/`,   lastModified: now, changeFrequency: 'monthly', priority: 0.8 },
-    { url: `${base}/about/`,      lastModified: now, changeFrequency: 'monthly', priority: 0.7 },
-    { url: `${base}/support/`,    lastModified: now, changeFrequency: 'monthly', priority: 0.6 },
-    { url: `${base}/donate/`,     lastModified: now, changeFrequency: 'monthly', priority: 0.5 },
-    { url: `${base}/links/`,      lastModified: now, changeFrequency: 'monthly', priority: 0.4 },
+    { url: `${base}/`,           lastModified: '2025-10-05', changeFrequency: 'weekly',  priority: 1.0 },
+    { url: `${base}/downloads/`, lastModified: '2025-10-05', changeFrequency: 'weekly',  priority: 0.9 },
+    { url: `${base}/features/`,  lastModified: '2025-10-05', changeFrequency: 'monthly', priority: 0.8 },
+    { url: `${base}/about/`,     lastModified: '2025-10-05', changeFrequency: 'monthly', priority: 0.7 },
+    { url: `${base}/support/`,   lastModified: '2025-10-05', changeFrequency: 'monthly', priority: 0.6 },
+    { url: `${base}/donate/`,    lastModified: '2025-10-05', changeFrequency: 'monthly', priority: 0.5 },
+    { url: `${base}/links/`,     lastModified: '2025-10-05', changeFrequency: 'monthly', priority: 0.4 },
   ]
 }