Include team slug in 404 error when adding team to project

When adding a non-existent team to a project via the API, the response is:

{"detail": "Team does not exist."}

The error omits which team slug triggered the failure. This is particularly painful for API consumers making bulk calls (e.g. via Terraform) that attempt to add multiple teams to a project in sequence — when one fails, there is no way to identify the offending team from the error response alone without cross-referencing request logs.

Suggested improvement: include the team slug in the detail message, e.g.:

{"detail": "Team 'backend-eng' does not exist."}

Action taken on behalf of Karan Pujji.

Start at the API entry point that adds a team to a project and trace the path producing the “Team does not exist.” 404 response. Update the response so it includes the requested team slug, then verify that missing-team requests return the proposed detail message without changing successful additions.