1.2.0

• Added opt-in staging preview through the staging: argument on
  reRuneSetup(...). It defaults to false and applies only to the current
  setup session.
• Added reRuneSetStagingMode(_:) for switching modes and synchronizing
  immediately after setup. Added reRuneIsStagingModeEnabled for reading the
  active mode. Calling the setter before setup throws
  ReRuneStagingModeError.setupRequired.
• Staging synchronization now applies complete locale snapshots, so draft
  additions, edits, deletions, disabled values, and never-published keys are
  reflected on the next successful sync.
• Staging and production state are isolated. A mode change restores the
  selected mode's cached content, and results from superseded update checks are
  discarded instead of crossing between modes.