Fix cube transition direction on forward history navigation

popstate always passed back=true, so going forward after back still
rotated the cube backwards. Track an incrementing idx in history.state
and only mirror the transition when the target entry is actually behind;
replaceState calls now preserve the state object instead of wiping it.

frontend/src/AnalyticsView.vue

@@ -126,7 +126,7 @@ const readStats = computed(() => calcReadStats(visits.value))
 watch(range, (r) => {
   const url = new URL(location.href)
   url.hash = r
-  history.replaceState(null, '', url)
+  history.replaceState(history.state, '', url)
 })
 
 const clients = computed(() => data.value?.clients || {})