v0.8.2: Accurate live-session freshness and stale-session eviction

Fixed — live dashboard session freshness

• The Windows polling fallback now applies the same --stale cutoff as initial
  discovery, so old transcript archives no longer reappear as live sessions
  after the first poll.
• Watched sessions are removed as soon as their transcript activity crosses the
  cutoff, even when no filesystem event occurs. A later transcript write adds
  the session back normally.
• Session rows now label and display transcript activity age rather than the
  most recent analysis refresh, so an idle historical transcript can no longer
  look freshly active merely because AgentPulse re-analyzed it.