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/hero-illustration.svg

@@ -0,0 +1,10 @@
+<svg width="400" height="300" viewBox="0 0 400 300" fill="none" xmlns="http://www.w3.org/2000/svg">
+  <rect width="400" height="300" fill="#f8fafc"/>
+  <rect x="50" y="50" width="300" height="200" rx="8" fill="white" stroke="#e5e7eb"/>
+  <rect x="80" y="80" width="240" height="20" rx="4" fill="#2563eb"/>
+  <rect x="80" y="120" width="180" height="12" rx="2" fill="#6b7280"/>
+  <rect x="80" y="140" width="200" height="12" rx="2" fill="#6b7280"/>
+  <rect x="80" y="160" width="160" height="12" rx="2" fill="#6b7280"/>
+  <circle cx="300" cy="180" r="40" fill="#3b82f6" opacity="0.2"/>
+  <circle cx="300" cy="180" r="20" fill="#2563eb"/>
+</svg>