update example nginx config to match dev server

docs/example.nginx.conf

@@ -90,7 +90,7 @@ server {
     set $styleSrc   "'unsafe-inline' 'self' ${main_domain}";
 
     # connect-src restricts URLs which can be loaded using script interfaces
-    set $connectSrc "'self' https://${main_domain} ${main_domain} https://${api_domain} blob: wss://${api_domain} ${api_domain} ${files_domain}";
+    set $connectSrc "'self' https://${main_domain} ${main_domain} https://${api_domain} blob: wss://${api_domain} ${api_domain} ${files_domain} https://${sandbox_domain}";
 
     # fonts can be loaded from data-URLs or the main domain
     set $fontSrc    "'self' data: ${main_domain}";
@@ -124,6 +124,7 @@ server {
 
     # everything except the sandbox domain is a privileged scope, as they might be used to handle keys
     if ($host != $sandbox_domain) { set $unsafe 0; }
+    if ($uri ~ ^\/unsafeiframe\/inner\.html.*$) { set $unsafe 1; }
 
     # privileged contexts allow a few more rights than unprivileged contexts, though limits are still applied
     if ($unsafe) {