feat(staging): publish /odoo-staging-environment/ guide page

New standalone page answering 'odoo staging environment': what staging is,
how odoo.sh's staging branches work (sourced to odoo.sh's own docs and
pricing page), why most small businesses do not need one, and the
back-up-install-test route we offer instead.

- Built on the newest page pattern (top bar, band rhythm, hero, FAQ,
  language switcher, footer), page-scoped CSS only; no new framework.
- ICP review R1-R7 applied: backup plan-gate and slot limit stated,
  the 'ask us' claim resolved against the Side Hustle limit, the restore
  stated as a rollback of live work, the restore routed through support,
  the meta de-claims 'one-click ... safely', 'module' defined at first
  use, and a scope/price boundary added to the escalation.
- Title 51 chars, meta 148; one H1; six FAQ pairs byte-identical to the
  FAQPage JSON-LD; @graph WebPage+Article+FAQPage+BreadcrumbList parses.
- CTA -> support.html#contact (existing route). og:image reuses the
  established hero share image.
- sitemap.xml + one llms.txt line; blog/index.json untouched.

sitemap.xml

@@ -60,6 +60,12 @@
     <changefreq>monthly</changefreq>
     <priority>0.6</priority>
   </url>
+  <url>
+    <loc>https://odoo4projects.com/odoo-staging-environment/</loc>
+    <lastmod>2026-11-01</lastmod>
+    <changefreq>monthly</changefreq>
+    <priority>0.6</priority>
+  </url>
   <url>
     <loc>https://odoo4projects.com/support.html</loc>
     <lastmod>2026-10-27</lastmod>