Make the Back button aware of client-side navigation

document.referrer only changes on full page loads, so the button sent
visitors to the home page instead of back after navigating within the
site. Use the Navigation API's canGoBack, which only considers this
site's history entries, and keep the referrer check as a fallback.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/components/ui/back.tsx

@@ -1,27 +1,32 @@
 "use client"
 
-import { useLocale, useTranslations } from "next-intl"
-import { useRouter } from "next/navigation"
+import { useTranslations } from "next-intl"
 import { FaArrowLeft } from "react-icons/fa"
 
+import { useRouter } from "@/i18n/navigation"
+
 import * as styles from "./back.module.css"
 
+// document.referrer only reflects the last full page load, so it misses
+// client-side navigations within the site. Only used where the Navigation
+// API isn't supported
+const cameFromThisSite = () =>
+  document.referrer !== "" &&
+  new URL(document.referrer).origin === window.location.origin
+
 const Back = () => {
-  const locale = useLocale()
   const router = useRouter()
   const t = useTranslations("buttons")
 
   const handleBack = () => {
-    const currentDomain = window.location.hostname
-    const referrer = document.referrer
+    // The Navigation API only lists this site's own history entries, so
+    // canGoBack is true exactly when the previous page was on this site
+    const canGoBack = window.navigation?.canGoBack ?? cameFromThisSite()
 
-    const isSameDomain =
-      referrer && new URL(referrer).hostname === currentDomain
-
-    if (window.history.length > 1 && isSameDomain) {
-      window.history.back()
+    if (canGoBack) {
+      router.back()
     } else {
-      router.push(`/${locale}`)
+      router.push("/")
     }
   }