Fix home regeneration (#6251)

* Fix regeneration marker not being removed after completion

* Return HTTP 206 from /api/v1/timelines/home if regeneration in progress
Prioritize RegenerationWorker by putting it into default queue

* Display loading indicator and poll home timeline while it regenerates

* Add graphic to regeneration message

* Make "not found" indicator consistent with home regeneration

app/services/precompute_feed_service.rb

@@ -3,5 +3,6 @@
 class PrecomputeFeedService < BaseService
   def call(account)
     FeedManager.instance.populate_feed(account)
+    Redis.current.del("account:#{account.id}:regeneration")
   end
 end