Serialize poll limits in instance serializer and initial state

app/serializers/initial_state_serializer.rb

@@ -3,7 +3,7 @@
 class InitialStateSerializer < ActiveModel::Serializer
   attributes :meta, :compose, :accounts,
              :media_attachments, :settings,
-             :max_toot_chars
+             :max_toot_chars, :poll_limits
 
   has_one :push_subscription, serializer: REST::WebPushSubscriptionSerializer
 
@@ -11,6 +11,15 @@ class InitialStateSerializer < ActiveModel::Serializer
     StatusLengthValidator::MAX_CHARS
   end
 
+  def poll_limits
+    {
+      max_options: PollValidator::MAX_OPTIONS,
+      max_option_chars: PollValidator::MAX_OPTION_CHARS,
+      min_expiration: PollValidator::MAX_EXPIRATION,
+      max_expiration: PollValidator::MIN_EXPIRATION,
+    }
+  end
+
   def meta
     store = {
       streaming_api_base_url: Rails.configuration.x.streaming_api_base_url,