fix: restore default domains and reset proxy ports on vhost enable

Re-enabling vhost (via `proxy:enable`, `domains:enable`, or `domains:add` with no global VHOST) was leaving the app pinned to the random high port and the empty VHOST file from the previous disabled state, so the new catch-all vhost intercepted requests for the app's domain. The `domains-enable` trigger now restores default vhosts via `domains_enable`, and `pre-enable-vhost` clears any stored proxy ports so they can be recomputed to 80/443. Also fixes the netrc lookup in the `git:auth` test to read dokku's netrc file directly.

plugins/domains/domains-enable

@@ -9,9 +9,9 @@ trigger-domains-domains-enable() {
   declare APP="$1" RESTART_APP="$2"
 
   if [[ "$RESTART_APP" == "true" ]]; then
-    enable_app_vhost "$APP"
+    domains_enable "$APP"
   else
-    enable_app_vhost "$APP" --no-restart
+    domains_enable "$APP" --no-restart
   fi
 }