v0.18.6

Fixed

• Giant-session freeze. The live viewer fully read and parsed the
  selected session; with today's large sessions (100MB+) that spiked
  ~700MB RSS on selection and froze the TUI (unresponsive to Ctrl+C/q).
  It now loads only a recent window (the last 8MB, snapped to a turn
  boundary) of a session file — bounded memory regardless of file size
  (104MB session: ~700MB → 40MB transient, ~200MB → 17MB retained). Full
  history is unchanged in report / summary; the viewer's scrollback
  is bounded to the recent window. Completes the v0.18.5 cache fix, which
  only addressed multi-session accumulation.