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/assets/images/devigo-logo.svg

@@ -0,0 +1,5 @@
+<svg width="40" height="40" viewBox="0 0 40 40" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <rect width="40" height="40" rx="8" fill="#2563eb"/>
+  <path d="M12 12h6c4.4 0 8 3.6 8 8s-3.6 8-8 8h-6V12z" fill="white"/>
+  <circle cx="15" cy="20" r="2" fill="#2563eb"/>
+</svg>