Assign an owner to each Inbox contact

Add a way to assign a team member as the responsible owner for each contact or conversation in Inbox/Messages.

The assigned owner should be visible in the conversation details and inbox list, with filters to show contacts assigned to a specific teammate or unassigned contacts. Team members should be able to reassign ownership when needed.

This would make it much easier for teams to divide inbound conversations, avoid duplicate replies, and maintain clear accountability for follow-ups.