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

go.mod

@@ -3,12 +3,14 @@ module github.com/insertr/insertr
 go 1.24.6
 
 require (
+	github.com/go-chi/chi/v5 v5.2.3
+	github.com/go-chi/cors v1.2.2
 	github.com/golang-jwt/jwt/v5 v5.3.0
-	github.com/gorilla/mux v1.8.1
 	github.com/lib/pq v1.10.9
 	github.com/mattn/go-sqlite3 v1.14.32
 	github.com/spf13/cobra v1.8.0
 	github.com/spf13/viper v1.18.2
+	github.com/yuin/goldmark v1.7.8
 	golang.org/x/net v0.43.0
 )
 
@@ -26,7 +28,6 @@ require (
 	github.com/spf13/cast v1.6.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/subosito/gotenv v1.6.0 // indirect
-	github.com/yuin/goldmark v1.7.8 // indirect
 	go.uber.org/atomic v1.9.0 // indirect
 	go.uber.org/multierr v1.9.0 // indirect
 	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect