Add the option for changing the contact/conversation sidebar items order

Editor assessment

The subject states the feature concretely, users can reorder contact and conversation sidebar items, with feat as the right type. But a reordering feature raises questions the message ignores entirely: is the order persisted per user, how is dragging implemented, and what happens to defaults? No scope, no body, no footers, so the diff carries every one of those answers. Hygiene is good: imperative shape, no trailing period, no junk, though the subject runs slightly long. Clear headline, absent substance, the standard acceptable profile.