Add sol call transcripts CLI and remove sol cluster
Add 4 Typer CLI commands (scan, segments, read, stats) in
apps/transcripts/call.py wrapping existing think.cluster functions
for terminal use. Remove the legacy sol cluster command (argparse
main() in think/cluster.py) and its registration in sol.py. Update
docs/THINK.md references. Update test_cluster_full.py to call
public API directly.