web: PRO needs a proven address — email verification gates the studio

A signed-in account is served exactly like a guest until it opens the
verification link: watermarked 2048px export, no saving, no PRO frames,
GPS stamp or HDF. SMTP is declared in .env; with SMTP_HOST unset the link
goes to the container log. Allowlisted admins count as verified.

docker/frontend/nginx.conf

@@ -32,7 +32,10 @@ server {
     set $api_upstream http://api:3000;
     proxy_pass $api_upstream$request_uri;
     proxy_http_version 1.1;
-    proxy_set_header Host $host;
+    # $http_host, not $host: keep the port when the visitor hits this container
+    # directly (localhost:8090), since the API builds the verification link from
+    # the forwarded host.
+    proxy_set_header Host $http_host;
     proxy_set_header X-Real-IP $remote_addr;
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     # Hand the API the scheme the visitor actually used (TLS is terminated by