address comments

app/models/ability.rb

app/models/concerns/cache_markdown_field.rb

app/models/concerns/mentionable.rb

app/models/concerns/participable.rb

app/models/note.rb

app/services/notes/post_process_service.rb

app/services/notes/slash_commands_service.rb

app/services/notification_service.rb

app/views/notify/note_personal_snippet_email.html.haml

app/views/notify/note_personal_snippet_email.text.erb

lib/banzai/filter/user_reference_filter.rb

spec/lib/banzai/filter/user_reference_filter_spec.rb

spec/models/ability_spec.rb

spec/models/concerns/mentionable_spec.rb

spec/models/note_spec.rb

spec/services/notes/create_service_spec.rb