fix(ui): file tree scroll position is stable when browsing

app/pages/package-code/[[org]]/[packageName]/v/[version]/[...filePath].vue

@@ -29,6 +29,31 @@ const parsedRoute = computed(() => {
 
 const packageName = computed(() => parsedRoute.value.packageName)
 const version = computed(() => parsedRoute.value.version)
+
+// Preserve file-tree scroll position across navigation within same package (+ version)
+const fileTreeKey = computed(() => `${packageName.value}@${version.value}`)
+const fileTreeSidebarRef = useTemplateRef('file-tree-sidebar')
+const savedFileTreeSidebarScroll = useState('code-sidebar-scroll', () => ({
+  key: '',
+  scrollTop: 0,
+}))
+
+onBeforeUnmount(() => {
+  savedFileTreeSidebarScroll.value = {
+    key: fileTreeKey.value,
+    scrollTop: fileTreeSidebarRef.value?.scrollTop ?? 0,
+  }
+})
+
+watch(
+  fileTreeSidebarRef,
+  fileTreeSidebarElement => {
+    if (fileTreeSidebarElement && savedFileTreeSidebarScroll.value.key === fileTreeKey.value)
+      fileTreeSidebarElement.scrollTop = savedFileTreeSidebarScroll.value.scrollTop
+  },
+  { once: true, flush: 'post' },
+)
+
 const filePathOrig = computed(() => parsedRoute.value.filePath)
 const filePath = computed(() => parsedRoute.value.filePath?.replace(/\/$/, ''))
 
@@ -349,6 +374,7 @@ defineOgImageComponent('Default', {
     <div v-else-if="fileTree" class="flex flex-1" dir="ltr">
       <!-- File tree sidebar - sticky with internal scroll -->
       <aside
+        ref="file-tree-sidebar"
         class="w-64 lg:w-72 border-ie border-border shrink-0 hidden md:block bg-bg-subtle sticky top-25 self-start h-[calc(100vh-7rem)] overflow-y-auto"
       >
         <CodeFileTree