feat: Removed hq signup page

adminsite/Dockerfile

@@ -26,6 +26,11 @@ ENV NEXT_PUBLIC_PADDLE_CLIENT_TOKEN=$NEXT_PUBLIC_PADDLE_CLIENT_TOKEN
 ARG NEXT_PUBLIC_PADDLE_ENV=sandbox
 ENV NEXT_PUBLIC_PADDLE_ENV=$NEXT_PUBLIC_PADDLE_ENV
 
+# Marketing site origin. Signup lives there (/start), not here; empty renders no
+# link at all rather than one that 404s.
+ARG NEXT_PUBLIC_SITE_URL=
+ENV NEXT_PUBLIC_SITE_URL=$NEXT_PUBLIC_SITE_URL
+
 RUN npm run build
 
 FROM node:26-alpine AS runner