fix(H-09): add hashchange event listener to Router.init() -- direct URL navigation now updates the view

frontend/js/router.js

@@ -53,12 +53,16 @@ const Router = {
   },
 
   init: () => {
-    window.addEventListener("popstate", () => {
+    // H-09 FIX: listen to both popstate (browser back/forward) AND
+    // hashchange (direct URL entry, anchor link clicks). Both are needed
+    // for a hash-router. popstate alone misses direct URL navigation.
+    const _handleNav = () => {
       const hash = window.location.hash.slice(1) || "/";
       Router.navigate(hash, false);
-    });
-    const hash = window.location.hash.slice(1) || "/";
-    Router.navigate(hash, false);
+    };
+    window.addEventListener("popstate",   _handleNav);
+    window.addEventListener("hashchange", _handleNav);
+    _handleNav();
   },
 };