Make human readable output default, move json output to --json

### What would you like the software to do?

Currently the tool outputs json, but we want to default to human readable format, ideally plaintext but we could also support an html report output. We should not remove the json output; just move it to behind a flag output --json

Start at the command-line reporting path that currently emits JSON and trace how output format is selected. Done means human-readable output is the default while JSON remains available through the --json flag; clarify whether plaintext or HTML is expected before implementing.

Written by the indexing model from the issue text.