Show relevant list of users in @mention dropdown

[ori-near]

Problem

Currently, the @mention dropdown on DevHub displays all users from near social when composing a comment on a proposal. This makes it difficult for users to find relevant collaborators, especially in discussion with many participants.

User Story

As a DevHub user who comments on proposals, I want the @mention dropdown to prioritize users most relevant to the current discussions, such as the proposal author and recent commenters, so I can find and tag the right people and collaborate more efficiently.

Acceptance Criteria

• [ ] When a user types "@" while composing a comment on a proposal, the dropdown prioritizes users relevant to the discussion
  • [ ] First: The proposal's author
  • [ ] Second: Users who ave recently commented on the proposal (in descending order by the comment date)
• [ ] If there are no relevant users (e.g. the user is the first comment), the dropdown displays all DevHub users in alphabetical order

Note: It would be nice if the dropdown could prioritize users the current interacts with most frequently on the DevHub platform, but if this is more complex we can skip it for now.