DIS-006: be get file: from a legacy elided store crashes

Some older stores use the legacy "elided" layout: the wtlog row-0 anchor has an empty project segment (file:/…/.be/) and refs/wtlog are regular files directly under .be/ with no <project>/ shard dir. be get file:<legacy-store> into an empty dir wires the cwd as a secondary worktree, then crashes because the secondary-wt path assumes the modern shard layout. The goal is either to migrate the elided layout or to materialize a modern shard on clone. Not hit in normal use today — be get file:<gitrepo> is the working path. See Store, Home, Submodules.

Issues

The secondary-wt path does not handle empty-project stores.

Blockers

None; needs a decision between migrating the elided layout in place or materializing a modern shard from it on clone.

Planned

Pick a path and pin a repro.

Landed

The fresh-init crash and the git-repo route.