Add "mark as unread" for a message or tribe

[ecurrencyhodler]

I would love a "mark as unread" feature for the sphinx app. This will help remind me to go back to texts and messages I receive in the sphinx tribe.

v1 doesn't have to pinpoint the exact message that I want as marked as unread. But it can simply mark the DM or Tribe group as unread.

Below is an example of what it could look like from a UI perspective taken from apple messages.

https://github.com/stakwork/sphinx-mac/assets/32662508/85c8fb16-2714-48b2-ba7f-a3a51d91c877