Remote git checks for cloud and teleport sessions respect the session's scope

What

Cloud and teleport sessions run Claude Code on a remote machine, seeded from your local project. The git checks involved now respect the session's scope.

• Branch-on-remote check: the lookup that finds which ancestor commit has already been pushed now takes sessionRoot and sessionReach and sets up git's environment for them. sessionRoot is the session's root folder, and sessionReach is the set of locations the session may use. Before, git ran with a fixed environment. If the reach cannot be established, the check now returns unknown.
• First upload: first upload (checkoutFirstUpload) now treats a no_git_dir state, where no git directory is found, the same way as an irregular one, and logs a description of it. Before, only irregular was handled.
• Remote probes: the remote probes made during first upload also pass sessionRoot and sessionReach.

Why

These git checks now run against the right folder and the right set of locations for the session. Seeding a cloud session is more robust when the project has no git directory. Where the session's scope can't be worked out, the result is unknown rather than a guess.