feat(site): implement dynamic client OS negotiation for Hero and CTA download buttons

site/src/sections/CTA.tsx

@@ -3,9 +3,11 @@ import { Crosshair } from '../components/Crosshair'
 import { WaveBars } from '../components/WaveBars'
 import { GlowButton } from '../components/GlowButton'
 import { useI18n } from '../i18n'
+import { useClientOS } from '../hooks/useClientOS'
 
 export function CTA() {
-  const { t } = useI18n()
+  const { t, locale } = useI18n()
+  const clientOS = useClientOS()
 
   return (
     <section className="relative py-28 md:py-36 overflow-hidden">
@@ -47,15 +49,23 @@ export function CTA() {
           </div>
         </div>
 
-        <div>
+        <div className="flex flex-col items-center gap-3">
           <GlowButton
-            href="#download"
+            href={clientOS.downloadUrl}
+            download={clientOS.downloadFilename || undefined}
             variant="primary"
             size="lg"
             className="shadow-glow-md hover:shadow-glow-lg"
           >
-            {t.cta.downloadBtn}
+            {locale === 'ko' ? clientOS.buttonLabelKo : clientOS.buttonLabelEn}
           </GlowButton>
+          <div className="flex items-center gap-2 font-mono text-xs text-neutral-400">
+            <span>{locale === 'ko' ? clientOS.subtextKo : clientOS.subtextEn}</span>
+            <span>·</span>
+            <a href="#download" className="underline hover:text-brand-amber transition-colors">
+              {locale === 'ko' ? '다른 OS 다운로드' : 'Other Platforms'}
+            </a>
+          </div>
         </div>
 
         <p className="font-mono text-nano text-neutral-500 mt-8 uppercase tracking-widest">