PR #2554 made these configurable via config.yaml but didn't add them
to DEFAULT_CONFIG or the config display. Users couldn't discover the
new knobs without reading the source.
- threshold: 0.80 (compress at 80% context usage)
- target_ratio: 0.40 (preserve 40% of context as recent tail)
- protect_last_n: 20 (keep last 20 messages uncompressed)
- Updated hermes config display to show all three fields