Fix worktree clone to configure upstream branch tracking

[Boomatang]

Closes #80

Summary

When git-grab clones a repository in the default worktree (bare) mode, the resulting repository now configures per-branch upstream tracking so that git pull and git push work out of the box without manual --set-upstream-to configuration.

Three new post-clone configuration steps are added to the worktree flow:

• Enable core.logallrefupdates so reflogs are maintained in the bare repository, matching non-bare clone behavior.
• Set branch.autoSetupMerge to always so that future branches created from remote refs automatically configure their upstream tracking.
• After fetching, iterate all local branches and explicitly set branch.<name>.remote and branch.<name>.merge to point at origin and refs/heads/<name> respectively. This ensures every branch present at clone time has correct tracking information.

Acceptance Criteria

The issue states that after grab git@github.com:user/repo.git, running git pull inside a worktree should work without requiring manual git branch --set-upstream-to commands.

This is addressed in two ways:

1. Existing branches at clone time are covered by setLocalTracking, which runs after fetchOrigin and configures branch.<name>.remote and branch.<name>.merge for every local branch.
2. Future branches are covered by setting branch.autoSetupMerge=always, so any new branch created from a remote-tracking ref will automatically inherit the correct upstream configuration.