feat(website): bilingual i18n (English default, Danish at /da) + SEO

Add @nuxtjs/i18n: English is the default locale (no prefix), Danish lives
under /da (prefix_except_default). Both server-rendered and indexed with
hreflang alternates + per-locale canonical (useLocaleHead in app.vue).
First-visit browser language is auto-detected and remembered in the
i18n_redirected cookie (redirectOn root).

- Keep the hand-authored COPY object; useLang/useCopy now read the i18n
  locale; useLocalizeHref/useLangToggle added. Every internal link is
  localized so navigation stays in-locale.
- Clear segmented EN|DA language switcher (active segment filled) replacing
  the ambiguous "en · da" pill.
- SEO: useSeoMeta defaults are locale-aware; og:image switches per locale
  (English / Danish share card); favicon links; robots.txt + sitemap.xml;
  env-aware siteUrl/baseUrl (localhost in dev, dezky.eu in prod).
- Update the cookie policy (dezky-lang -> i18n_redirected).
- Gate the Traefik wss:443 HMR behind DEZKY_TRAEFIK so localhost dev/DevTools
  connect over plain ws (fixes the DevTools disconnect loop).

apps/website/components/landing/PageHeader.vue

@@ -8,12 +8,13 @@ defineProps<{ label: string, title: string, intro?: string }>()
 
 const t = useTheme()
 const copy = useCopy()
+const localePath = useLocalePath()
 </script>
 
 <template>
   <LandingContainer pad="clamp(56px, 8vw, 120px) clamp(20px, 5vw, 64px) 0">
     <NuxtLink
-      to="/"
+      :to="localePath('/')"
       :style="{ fontFamily: '\'JetBrains Mono\', monospace', fontSize: '12px', color: t.fgMuted, letterSpacing: '0.04em', display: 'inline-flex', alignItems: 'center', gap: '8px' }"
     >← {{ copy.pages.back }}</NuxtLink>