fix: preserve all domains when renaming an app

The `post-app-rename-setup` trigger redirected `sed` output to the new
app's VHOST file inside a loop over global vhosts, so each iteration
clobbered the previous one and only the last global subdomain was
rewritten. When no global vhost was set, the loop never ran and the
new app's VHOST file was never written, leaving the renamed app with
no domains.

Copy the old app's VHOST file once as a baseline, then apply `sed -i`
in place for each global vhost so substitutions accumulate. Guard
against a missing global VHOST file and skip blank lines.

plugins/domains/post-app-rename-setup

@@ -7,11 +7,20 @@ trigger-domains-post-app-rename-setup() {
   declare trigger="post-app-rename-setup"
   declare OLD_APP="$1" NEW_APP="$2"
 
-  if [[ -f "$DOKKU_ROOT/$OLD_APP/VHOST" ]]; then
-    while read -r VHOST || [[ -n "$VHOST" ]]; do
-      sed -e "s/$OLD_APP.$VHOST/$NEW_APP.$VHOST/g" "$DOKKU_ROOT/$OLD_APP/VHOST" >"$DOKKU_ROOT/$NEW_APP/VHOST"
-    done <"$DOKKU_ROOT/VHOST"
+  if [[ ! -f "$DOKKU_ROOT/$OLD_APP/VHOST" ]]; then
+    return
   fi
+
+  cp -f "$DOKKU_ROOT/$OLD_APP/VHOST" "$DOKKU_ROOT/$NEW_APP/VHOST"
+
+  if [[ ! -f "$DOKKU_ROOT/VHOST" ]]; then
+    return
+  fi
+
+  while read -r VHOST || [[ -n "$VHOST" ]]; do
+    [[ -z "$VHOST" ]] && continue
+    sed -i -e "s/${OLD_APP}\.${VHOST}/${NEW_APP}.${VHOST}/g" "$DOKKU_ROOT/$NEW_APP/VHOST"
+  done <"$DOKKU_ROOT/VHOST"
 }
 
 trigger-domains-post-app-rename-setup "$@"