fix(landing-page): correct nav-icon comment to match actual responsive behaviour

The JSX comment introduced for the new Discord + X icon buttons in
PR #3230 claimed the icons "survive at narrow widths while text-only
nav items get pushed off". The CSS that shipped in the same PR does
the opposite: both `@media (max-width: 1080px)` and `@media (max-width:
880px)` blocks add `.nav-side .nav-icon { display: none; }`, so at
narrow widths the icons collapse alongside the ghost Download CTA
while the text nav <ul> moves into the hamburger panel — only the
Star CTA remains visible in the bar.

Rewrite the comment to describe the actual responsive contract so
the next reader of `header.tsx` doesn't have to cross-reference
`globals.css` to figure out which surface stays. Reviewer flag from
@PerishCode on PR #3230.

No code-path change; comment-only.

apps/landing-page/app/_components/header.tsx

@@ -280,8 +280,10 @@ export function Header({
             Discord + X icon buttons live before Download / Star so the
             community channels are reachable from every page without
             burning a nav text slot. The icons are aria-labeled and
-            otherwise unlabeled — at narrow widths they survive while
-            text-only nav items get pushed off.
+            otherwise unlabeled. At ≤1080px they collapse alongside the
+            ghost Download CTA and the text-only nav <ul> (the latter
+            moves into the hamburger panel) — only the Star CTA stays
+            visible in the bar.
           */}
           <a
             className='nav-icon'