feat(website): gated coming-soon holding page with email signup

Add a standalone bilingual /coming-soon page (branded, dark, email signup
via mailto:info@dezky.eu, fires a waitlist-signup Umami event, noindex) plus
a global middleware that redirects every route to the locale-correct holding
page while NUXT_PUBLIC_COMING_SOON=true.

- Env-gated (default off, so dev and the live site are unaffected); flip the
  env in Coolify to show/hide the holding page with no code change.
- Preview the real site behind the gate via ?preview=<previewToken>
  (NUXT_PUBLIC_PREVIEW_TOKEN), which sets a 7-day cookie.
- Locale-preserving redirects (/da/* -> /da/coming-soon), no loops.

apps/website/nuxt.config.ts

@@ -76,6 +76,12 @@ export default defineNuxtConfig({
   runtimeConfig: {
     public: {
       siteUrl,
+      // Holding-page gate. Set NUXT_PUBLIC_COMING_SOON=true (Coolify env) to
+      // show the coming-soon page for every route; flip to false to launch.
+      // Preview the real site behind the gate with ?preview=<previewToken>
+      // (override the token via NUXT_PUBLIC_PREVIEW_TOKEN).
+      comingSoon: false,
+      previewToken: 'dezky-preview',
     },
   },