fix(theme): remove extra slash when concatenating base with sidebar links

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Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

src/client/theme-default/support/sidebar.ts

@@ -112,7 +112,8 @@ function addBase(items: SidebarItem[], _base?: string): SidebarItem[] {
   return [...items].map((_item) => {
     const item = { ..._item }
     const base = item.base || _base
-    if (base && item.link) item.link = base + item.link
+    if (base && item.link)
+      item.link = base + item.link.replace(/^\//, base.endsWith('/') ? '' : '/')
     if (item.items) item.items = addBase(item.items, base)
     return item
   })