v0.5.3

Fixed

• Child-session rollups no longer stop at a fixed 20-level depth: rootOf
  walks parent links to the true root, with a cycle guard instead of a cap.
• session.deleted aggregates instead of tombstoning: the deleted session's
  totals fold into its parent and the entry is dropped, so a long-lived server
  keeps no ledger entry per deleted session. Live children reparent to the
  grandparent, and a bounded window of deleted ids still swallows late events.
• Documented that the model context-limit cache lives for the process: provider
  config changes need a restart or TOKEN_NORM_CONTEXT_LIMIT.