v0.6.0: Reclaiming what ended sessions leave behind

• agent-ps prune removes the parts of an ended session that are not the
  conversation: subagent transcripts, file history, task records, shell
  snapshots, request dumps. On the machine it was written on that is 96M across
  43 sessions, against 33M for deleting every session older than a month,
  because the sessions holding the space are recent rather than old.
• It reports by default and removes only with --apply. Transcripts are never
  removed, a session with a running process is never touched whatever its age,
  and agents that keep sessions in a database are left alone entirely.
• p in the table does the same for the selected row, after a confirmation
  naming what goes. On a running session it refuses and says why.
• The detail panel marks which parts of a session can be pruned, and the line
  above the keys reports the total when there is one.
• One confirmation path now serves every destructive key, rather than each
  growing its own.
• Release pages take their title and notes from the changelog instead of the
  commit list.