Feature: Contribution rooms around active missions

[sajeetharan]

Problem

A matched issue is currently a solo handoff. Developers cannot see who else is exploring it, ask focused questions, or coordinate without leaving DevGlobe.

Proposed solution

Create temporary, issue-scoped contribution rooms for accepted missions. A room shows public repository context, opted-in participants, relevant public experts, and maintainer responses.

Acceptance criteria

• Rooms are created only from a real public issue and expire after inactivity or closure.
• Joining is explicit; no inferred participation or private contact details.
• Participants can leave at any time.
• Messages and links are bounded, moderated, and scoped to the issue.
• Maintainer identity is verified before a response is labeled as maintainer feedback.
• Empty rooms still provide issue context and the next useful action.
• Track room joins, useful responses, contribution starts, and verified completions.

Success metric

Increase accepted-mission to verified-contribution conversion without encouraging duplicate work.

Related

#168 #210