Random matching for collaborations

Collaborations could benefit from a random matching feature.

When joining a game, there should be an option to pair with someone randomly. If enough people are in the random queue together to meet the player requirements for a game, then a game is created for them. Separate queues are maintained for each project hash.

No files, tests, or entry points are identified. Start by locating the collaboration and game-joining flow, then clarify queue isolation by project hash, player requirements, and game-creation behavior; done should include verified random pairing behavior.

Written by the indexing model from the issue text.