fix(scroll): clear URL hash when back-to-top is clicked

Uses history.pushState to strip the stale #entry-slug without
triggering a page jump, then smooth-scrolls to the top.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vgmzx8VTTTmCskSpQtsLTr

themes/intotheeast/templates/trip.html.twig

@@ -567,6 +567,7 @@ document.addEventListener('DOMContentLoaded', function () {
     var threshold = window.innerHeight * 0.8;
     var shown = false;
     btn.addEventListener('click', function () {
+        history.pushState(null, '', window.location.pathname + window.location.search);
         window.scrollTo({ top: 0, behavior: 'smooth' });
     });
     window.addEventListener('scroll', function () {