Migrate to Chi router and add Norwegian Devigo demo

Major improvements:
- Replace Gorilla Mux with Chi v5 router for better performance and cleaner code
- Fix CSS/JS MIME type issues that prevented proper asset loading
- Add built-in CORS middleware replacing manual OPTIONS handlers
- Simplify routing with nested route syntax
- Update URL parameter extraction from mux.Vars to chi.URLParam

New Devigo demo:
- Add production Norwegian sales training website (devigo.no)
- Real-world Hugo-generated content with TailwindCSS
- 39 insertr-enhanced elements for comprehensive CMS testing
- Demonstrates international language support and B2B use cases
- Fixed asset paths for localhost serving compatibility

Technical benefits:
- Automatic MIME type detection for static files
- Reduced code complexity with built-in middleware
- Better performance with lighter dependency stack
- Production-ready CORS handling

demos/devigo-web/public/sitemap.xml

@@ -0,0 +1 @@
+<?xml version="1.0" encoding="utf-8" standalone="yes"?><urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml"><url><loc>https://devigo.no/</loc></url><url><loc>https://devigo.no/categories/</loc></url><url><loc>https://devigo.no/authors/</loc></url><url><loc>https://devigo.no/sections/contact/</loc></url><url><loc>https://devigo.no/authors/patrick-rustan/</loc></url><url><loc>https://devigo.no/sections/</loc></url><url><loc>https://devigo.no/tags/</loc></url></urlset>