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/ProductMockup.vue

@@ -38,7 +38,9 @@ onMounted(() => {
   const parent = frame.value?.parentElement
   if (parent && typeof ResizeObserver !== 'undefined') {
     ro = new ResizeObserver(recompute)
-    ro.observe(parent)
+    // Cast via unknown: a dependency pulls a second DOM lib so HTMLElement and
+    // ResizeObserver's Element param resolve to non-overlapping types here.
+    ro.observe(parent as unknown as Element)
   }
 })
 onBeforeUnmount(() => ro?.disconnect())