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.

tests/unit/git_3.bats

@@ -100,7 +100,7 @@ teardown() {
   assert_success
   assert_output_contains "Setting netrc auth entry for host github.com"
 
-  run /bin/bash -c "netrc get github.com"
+  run /bin/bash -c "netrc get --netrc-file ${DOKKU_ROOT}/.netrc github.com"
   echo "output: $output"
   echo "status: $status"
   assert_success