⚡️ perf(build): remove sitemap generation to cut static export time (#15702)

* ⚡️ perf(build): remove sitemap generation to cut static export time

The sitemap accounted for 772 of 827 prerendered pages, each fetching
marketplace data at build time. Static generation drops from 28.2s to
0.3s and total next build from ~59s to ~32s.

* Redirect legacy sitemap URLs to the landing site

* Redirect sitemap index to landing sitemap

.gitignore

@@ -93,9 +93,6 @@ public/swe-worker*
 # Generated files
 src/app/spa/[variants]/[[...path]]/spaHtmlTemplates.ts
 public/*.js
-public/sitemap.xml
-public/sitemap-index.xml
-sitemap*.xml
 robots.txt
 
 # Git hooks