fix(nav): restore frosted glass on the portaled account popover

Now that the popover is portaled to body its backdrop-filter actually samples the content
behind it, so the near-opaque glass-menu (needed only as a workaround while blur was
trapped) made it look solid. Switch it back to the frosty .glass (78%); the working blur
softens the background so text stays readable without the bleed-through. Trapped header
menus (language/notifications) keep glass-menu.

frontend/src/components/NavSidebar.tsx

@@ -161,7 +161,7 @@ export default function NavSidebar({
                 <div className="fixed inset-0 z-40" onClick={() => setAcctOpen(false)} />
                 <div
                   style={{ position: "fixed", left: acctPos.left, bottom: acctPos.bottom }}
-                  className="glass-menu w-60 rounded-xl p-3 z-50 animate-[popIn_0.16s_ease]"
+                  className="glass w-60 rounded-xl p-3 z-50 animate-[popIn_0.16s_ease]"
                 >
                 <div className="flex items-center gap-3 pb-3 border-b border-border">
                   <AvatarImg