Mino chapter-05

Added

• Chapter 05 multiple sessions: /new, /sessions, /resume <id>, /clear, and
  /help. Each private JSONL file carries its session ID in its filename; startup
  restores the last selection from active-session.json.
• Interactive clearing requires the complete current session ID. It keeps other
  sessions, configuration, SOUL, and recovery backups; it does not undo commands or
  promise secure disk erasure.
• The single conversation left by Chapters 02–04 is selected in place on first
  start, because it already lives in ~/.mino/sessions/; nothing is copied.

Changed

• Serialize session commands and Agent turns with the store-wide sessions.lock.
  Selection damage, or a missing selection with several sessions, enters a
  command-only recovery state; storage write failures stop chat.
• Publish selection and clearing atomically after syncing temporary files, then
  sync their directory before advancing memory. Tool protocol and record versions
  remain unchanged. Existing SOUL files remain untouched.