function switchSectionTab(btn, panelId) {
    // Tab selection uses .is-selected (charter); panel visibility
    // still uses .active (display: none/block toggle).
    document.querySelectorAll('.project-sections .section-tab').forEach(function(t) { t.classList.remove('is-selected'); });
    document.querySelectorAll('.project-sections .section-panel').forEach(function(p) { p.classList.remove('active'); });
    btn.classList.add('is-selected');
    var panel = document.getElementById(panelId);
    if (panel) panel.classList.add('active');
    history.replaceState(null, '', '#' + panelId);
}
(function() {
    var hash = window.location.hash.replace('#', '');
    if (hash) {
        var panel = document.getElementById(hash);
        var tab = document.querySelector('.project-sections [data-tab="' + hash + '"]');
        if (panel && tab) switchSectionTab(tab, hash);
    }
})();