feat(website): fit the language menu on narrow screens

The menu's list opened leftward past the screen edge on phones, and at
320px the fourth header button overlapped the brand. Open the list to the
right below 640px, and hide the GitHub star count below 360px when a page
has a language menu.

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

website/public/assets/styles.css

@@ -2650,6 +2650,10 @@ main:not(.container) > .translation-notice {
   margin-inline: auto;
 }
 @media (max-width: 640px) {
+  .language-list {
+    right: auto;
+    left: 0;
+  }
   .language-current {
     position: absolute;
     width: 1px;
@@ -2662,3 +2666,9 @@ main:not(.container) > .translation-notice {
     width: calc(100% - 2.5rem);
   }
 }
+/* The language menu adds a fourth header button; make room beside the brand. */
+@media (max-width: 359px) {
+  .header-social:has(.language-menu) .nav-github-count {
+    display: none;
+  }
+}