fix: use <details>/<summary> for Pug language picker to get native toggle

The manual JS click-handler approach (tried with stopPropagation,
containment check, and mousedown variants) never worked reliably on
login/password/settings pages. The browser's native <details>/<summary>
toggle behaviour requires no JavaScript and is immune to Bootstrap JS or
React event delegation interference.

The inline script now only builds the return_to hrefs and handles
outside-click-to-close (setting details.open=false). The CSS gains a
.language-picker-details rule that sets position:relative so the
absolutely-positioned dropdown-menu is positioned correctly, and
details[open] .dropdown-menu { display: block } to show the menu.

The #language-picker-toggle id remains on the <summary> so the existing
CSS (cursor, text-decoration, material-symbols alignment) continues to
apply. The React LanguagePicker is unaffected.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/web/app/views/layout/language-picker.pug

@@ -1,9 +1,6 @@
 li.language-picker
-	.dropdown
-		button#language-picker-toggle.btn-inline-link(
-			type='button'
-			aria-haspopup='true'
-			aria-expanded='false'
+	details.language-picker-details
+		summary#language-picker-toggle.btn-inline-link(
 			aria-label=translate('select_a_language')
 			translate='no'
 		)
@@ -25,10 +22,9 @@ li.language-picker
 						)= settings.translatedLanguages[lngCode]
 	script.
 		(function () {
-			var toggle = document.getElementById('language-picker-toggle')
-			var menu = toggle && toggle.parentElement.querySelector('.dropdown-menu')
-			if (!toggle || !menu) return
-			// Build return_to at runtime so the href reflects the actual current path
+			var details = document.querySelector('.language-picker-details')
+			var menu = details && details.querySelector('.dropdown-menu')
+			if (!details || !menu) return
 			menu.querySelectorAll('a[data-lng]').forEach(function (a) {
 				var lng = a.getAttribute('data-lng')
 				a.href =
@@ -37,20 +33,10 @@ li.language-picker
 					'&return_to=' +
 					encodeURIComponent(window.location.pathname)
 			})
-			var picker = toggle.closest('.language-picker')
-			function close() {
-				menu.classList.remove('show')
-				toggle.setAttribute('aria-expanded', 'false')
-			}
-			toggle.addEventListener('click', function () {
-				var opening = !menu.classList.contains('show')
-				menu.classList.toggle('show', opening)
-				toggle.setAttribute('aria-expanded', String(opening))
-			})
-			document.addEventListener('mousedown', function (e) {
-				if (!picker || !picker.contains(e.target)) close()
+			document.addEventListener('click', function (e) {
+				if (!details.contains(e.target)) details.open = false
 			})
 			document.addEventListener('keydown', function (e) {
-				if (e.key === 'Escape') { close(); toggle.focus() }
+				if (e.key === 'Escape') details.open = false
 			})
 		})()

services/web/frontend/stylesheets/components/footer.scss

@@ -203,6 +203,7 @@ footer.site-footer {
   vertical-align: middle;
 }
 
+// Applies to both the React language picker toggle (button) and the Pug one (summary)
 #language-picker-toggle {
   text-decoration: none;
   cursor: pointer;
@@ -222,6 +223,28 @@ footer.site-footer {
   }
 }
 
+// Pug language picker uses <details>/<summary> for native toggle behaviour
+.language-picker-details {
+  display: inline-block;
+  position: relative;
+
+  summary {
+    list-style: none;
+
+    &::-webkit-details-marker {
+      display: none;
+    }
+
+    &::marker {
+      content: '';
+    }
+  }
+
+  &[open] .dropdown-menu {
+    display: block;
+  }
+}
+
 .language-picker .dropdown-menu {
   // Open upward — Popper.js isn't available on all page layouts
   top: auto;