feat: Show assigned hours inline with each user avatar

app/controllers/assignments_controller.rb

app/controllers/candidates_controller.rb

app/controllers/conferences_controller.rb

app/javascript/controllers/conference_workload_controller.js

app/models/assignment.rb

app/models/user.rb

app/views/assignments/_user_avatar.html.erb

app/views/candidates/_user_avatar.html.erb

app/views/conferences/show.html.erb