Remove explicit smooth scroll behavior from routing logic

This was potentially overriding a site's setting. Instead, we should
encourage users adding code like:

```
registerStyleBase("html") {
   Modifier.scrollBehavior(ScrollBehavior.Smooth)
}
```

in their own code instead, and leave the behavior up to per side.

frontend/kobweb-core/src/jsMain/kotlin/com/varabyte/kobweb/navigation/Router.kt

@@ -446,23 +446,20 @@ class Router {
                 // Even if the URL hasn't changed, still scroll to the target element if you can. Sometimes a user might
                 // scroll the page and then re-enter the same URL to go back.
                 if (url.contains('#')) {
-                    fun Element.scrollIntoViewSmoothly() {
-                        scrollIntoView(js("{behavior: \"smooth\"}"))
-                    }
-
+                    fun scrollElementIntoView() = document.getElementById(url.substringAfter('#'))?.scrollIntoView()
                     if (onNewPage) {
                         // We need to give the page a chance to render first, or else the element with the ID might not
                         // exist yet.
                         MutationObserver { mutations, observer ->
                             mutations.forEach { mutation ->
                                 if (mutation.type == "childList") {
-                                    document.getElementById(url.substringAfter('#'))?.scrollIntoViewSmoothly()
+                                    scrollElementIntoView()
                                     observer.disconnect()
                                 }
                             }
                         }.observe(document.body!!, MutationObserverInit(childList = true, subtree = true))
                     } else {
-                        document.getElementById(url.substringAfter('#'))?.scrollIntoViewSmoothly()
+                        scrollElementIntoView()
                     }
                 }
             }

playground/site/src/jsMain/kotlin/playground/MyApp.kt

@@ -31,6 +31,12 @@ fun updateTheme(ctx: InitSilkContext) = ctx.config.apply {
 
 @InitSilk
 fun registerGlobalStyles(ctx: InitSilkContext) = ctx.stylesheet.apply {
+    registerStyle("html") {
+        cssRule(CSSMediaQuery.MediaFeature("prefers-reduced-motion", StylePropertyValue("no-preference"))) {
+            Modifier.scrollBehavior(ScrollBehavior.Smooth)
+        }
+    }
+
     registerStyleBase("body") {
         Modifier
             .fontFamily(