feature: ux polish

[telcharr]

cargo capdiff can now write a capdiff.lock snapshot of the current capability sets, which is what --baseline was missing. there was no way to generate the file it diffs against before. Findings also now carry the dependency path that pulled the crate in now, so you get via ureq -> rustls -> ring instead of just the leaf. New explain <crate> command that dumps one crate's severity, rationale, dep path, and evidence. Added capdiff.toml for supressing findings you've already reviewed and overriding severity per crate. Suppressed ones still get counted in the report so nothing disappears quietly.

Schemas bump to audit v5 / diff v4, both gained suppressed_count and an optional dep_path.

Human output is colored now too. Strips itself when piped or under NO_COLOR