Signals' metrics by person and whose key paid (#278)

With the server paying for everyone's Signals, its bill had no names.
ipx_signals_judged_total, ipx_signals_hits_total and ipx_jev_tokens_total
now carry user (the account's name) and key (server or own); a call
shared on the server's key is split by each person's share of its
questions. Icon picks bill the person on the server's key, key checks on
their own. The dashboard has tokens and items by person and a Who used
what table over its range.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ipx/CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `/metrics` counts Signals: items judged and fitting, calls to Jev by how they ended, the time they took and the tokens TypeSafe counted, time since the judge's last pass, and keys refused; a failed call to Jev shows as a failed trace (#270, #275).
 - An admin setting for how many days back a new Signal reads (#276).
+- `/metrics` breaks Signals' items, fits and TypeSafe tokens out by person and by whose key paid, so the server's bill can be split (#278).
 - An admin setting, Signals for everyone on the server's TypeSafe key, so the server pays for Jev instead of each person (#271).
 
 ### Changed