Route tokens profile through checkpoint.Open

tokens profile was the one remaining production CLI path constructing a checkpoint store directly (checkpoint.NewGitStore) instead of going through checkpoint.Open, so a future settings-driven primary backend would be silently ignored there. Route it through Open and widen the report helpers from *checkpoint.GitStore to the checkpoint.PersistentStore interface.

benchutil keeps its direct NewGitStore (documented benchmark fixture that pins the v1 topology and never exercises backend selection).

No behavior change: Open with default options resolves the same v1 git store.