Sandboxes reach Linear through the workspace's Linear app

Before, every Linear task in a workspace borrowed a single member's read-only Linear grant, and if that member revoked it or reconnected from another Linear organization, Linear tasks stopped with auth_required until someone granted it again. That shared grant is gone, and the Linear settings card no longer shows a separate sandbox read-access line.

This is also a widening, so we say it plainly: the sandbox can now read whatever the Sinatra app can see in your Linear workspace, not only what one member could, and it can add comments and attachments to the task's own issue, and edit or reply to the comments Sinatra posted for this task. Tasks started from GitHub issues no longer get Linear access in their sandbox at all. Nothing else in Linear is writable from the sandbox. The person delegating still needs a linked or matched Linear identity and workspace membership.