Adds packages/vault-cli (the `vault` CLI: search/show/tree, clobber-safe
create/move/rename across both /vault and /data + manifest regen, sync-data,
report, analyze) and wires it onto $PATH via modules/hosts/core/vault.nix for
server + vault-client hosts. Scripts self-locate siblings via realpath so they
run from the Nix store. Includes the deterministic $0 report generator, the
topology-manifest generator, and the shared Librarian prompt.
