docs(testing): describe the Quorum eval lab accurately, replacing stale Drill references

The evals harness was renamed Drill -> Quorum and rewritten from
Python/uv to Bun/TypeScript; docs/testing.md and CLAUDE.md still
described the old tool. Beyond the rename, the old text also
misdescribed the system: quorum is the harness CLI, one part of the
eval lab — it drives real coding-agent CLIs through a Gauntlet QA
agent and grades against scenario acceptance criteria plus
deterministic post-checks. The quick start now matches the eval
repo's actual commands (bun install / bun run quorum run
scenarios/<name> --coding-agent claude; scenarios are directories,
not *.yaml) and points at the Live Eval Risk section before anyone
runs a permissive-mode session.

Drift reported in closed PR #2121 (@JFWaskin); that PR's replacement
quick start kept the uv commands, so this rewrite goes from the eval
repo's README instead.

CLAUDE.md

@@ -101,7 +101,7 @@ Skills are not prose — they are code that shapes agent behavior. If you modify
 
 ## Eval harness
 
-Skill-behavior evals live in [superpowers-evals](https://github.com/prime-radiant-inc/superpowers-evals/), cloned into `evals/` — see `evals/README.md` for setup. Drill (the harness) drives real tmux sessions of Claude Code / Codex / Gemini CLI and judges skill compliance with an LLM verifier. Plugin-infrastructure tests still live at `tests/`.
+Skill-behavior evals live in [superpowers-evals](https://github.com/prime-radiant-inc/superpowers-evals/), cloned into `evals/` — see `evals/README.md` for setup. Quorum (the harness CLI, one part of that eval lab) drives real coding-agent CLIs — Claude Code, Codex, Gemini, and others — through a Gauntlet QA agent and grades them against scenario acceptance criteria plus deterministic post-checks. Plugin-infrastructure tests still live at `tests/`.
 
 ## Understand the Project Before Contributing