Add post-sync hook (#1479)

app/models/concerns/syncable.rb

@@ -22,6 +22,10 @@ module Syncable
     raise NotImplementedError, "Subclasses must implement the `sync_data` method"
   end
 
+  def post_sync
+    # no-op, syncable can optionally provide implementation
+  end
+
   def sync_error
     latest_sync.error
   end