fix(ui): keep the sidebar's EN/VI buttons at full width beside the three theme buttons

The language row was a 4-column grid holding two buttons inside a flex-1 box. Once the theme row gained a third (System) button, that box narrowed and each language button fell below the width of its own label, so EN/VI sat off-centre and overflowed. One column per language, centred text.

client/src/components/Sidebar.tsx

@@ -520,7 +520,9 @@ export function Sidebar({ wsConnected, collapsed, onToggle }: SidebarProps) {
                 <p className="px-1 text-[10px] font-semibold uppercase tracking-wider text-fg-muted">
                   {t("nav:language")}
                 </p>
-                <div className="mt-2 grid grid-cols-4 gap-1">
+                {/* One column per language: a wider grid squeezed each button
+                    below the width of its own label once Theme grew a third. */}
+                <div className="mt-2 grid grid-cols-2 gap-1">
                   {SUPPORTED_LANGUAGES.map((language) => {
                     const active = language === currentLanguage;
                     return (
@@ -530,7 +532,7 @@ export function Sidebar({ wsConnected, collapsed, onToggle }: SidebarProps) {
                         aria-pressed={active}
                         aria-label={t(`nav:languageNames.${language}`)}
                         title={t(`nav:languageNames.${language}`)}
-                        className={`rounded-md px-2 py-1.5 text-[11px] font-semibold transition-colors ${
+                        className={`rounded-md px-1 py-1.5 text-center text-[11px] font-semibold transition-colors ${
                           active
                             ? "bg-accent/20 text-accent border border-accent/30"
                             : "bg-surface-1 text-fg-secondary border border-border hover:bg-surface-3 hover:text-fg-primary"