v0.18.7

Fixed

• Giant-session freeze, part 2: discovery. v0.18.6 bounded the
  viewer (the selected session), but the tree-discovery walk still read
  whole files on every refresh — peeking at the first line, the last ~50
  lines, and the latest user prompt by slurping the entire session. With
  100MB+ sessions on disk this re-read hundreds of MB every 2s and froze
  the TUI even when the giant session wasn't selected. Discovery now
  reads bounded head/tail slices (first 16KB / last 256KB–1MB) of
  oversized files. Measured: discoverSessions over a real ~/.claude
  with a 104MB session dropped from hundreds of MB to ~25MB. Steady-state
  memory is now flat regardless of session size.