Replace go-chi/chi with go-pkgz/routegroup

[paskal]

Summary

• Replace go-chi/chi router with go-pkgz/routegroup using standard http.ServeMux
• Replace chi middleware with go-pkgz/rest equivalents (RealIP, Throttle, NoCache)
• Add custom timeout middleware to replace chi's middleware.Timeout
• Use Go 1.22+ routing patterns (POST /path)
• Migrate golangci-lint config to v2 format