Loki Mode

Added

• 1-click rollback + checkpoint UX (R6 of the competitive arc): deterministic,
  obvious rollback so autonomous runs can be undone in one action. Enhances the
  existing checkpoint/rollback in place (no parallel system).
• loki rollback latest and loki rollback to <id> (plus loki rollback list):
  one-command restore of .loki/ state, with a per-iteration "you can undo this"
  signal and an automatic pre-rollback snapshot so a rollback is itself
  undoable ("undo your undo"); the snapshot id is printed for the user.
• Dashboard rollback control: 1-click restore with a confirm, surfacing the
  pre-rollback snapshot id in a notice so dashboard users can undo the undo too.

Fixed

• Rollback safety invariant: if the automatic pre-rollback snapshot fails,
  rollback now ABORTS by default (preserving current state) instead of silently
  proceeding to a destructive restore; pass --force to roll back without a
  safety snapshot. Proven by tests that assert state is preserved on snapshot
  failure.

Notes

• The .loki/ state restore is atomic (tmp + rename). Working-tree code restore
  is opt-in (--code / the surfaced git stash apply refs/loki/cp/<id>): a
  divergent apply aborts or shows conflict markers (exit 1), never a silent
  half-apply, so uncommitted work is protected.
• Council: 3-of-3 unanimous (round 2, after fixing the snapshot-failure safety
  invariant and surfacing the undo handle in the dashboard).
• NOT tested in this release: rollback across a force-pushed/rewritten git
  history; restoring newly-added (untracked) files (tracked-files scope is
  documented in the CLI output).