Remove admin-only gate on SMS subscription buttons

[moveson]

After verifying the SMS opt-in flow in staging (#1891), remove the admin-only gate so all users can access SMS subscriptions.

Changes needed:

• app/helpers/toggle_helper.rb: Remove the !current_user&.admin? check that shows "SMS temporarily out of service" for non-admin users
• spec/system/subscriptions/subscribe_to_effort_notifications_spec.rb: Convert pending SMS scenarios back to active scenarios
• spec/system/subscriptions/subscribe_to_person_notifications_spec.rb: Convert pending SMS scenarios back to active scenarios

Tracked by #1216.