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/service-worker.js

@@ -0,0 +1,10 @@
+importScripts(
+  "https://storage.googleapis.com/workbox-cdn/releases/6.0.2/workbox-sw.js"
+);
+
+workbox.setConfig({ debug: false });
+
+workbox.routing.registerRoute(
+  ({ request }) => request.destination === "image",
+  new workbox.strategies.NetworkFirst()
+);