feat(benchmarks): critic-email — turn the critique's own example into a safety task

[ousamabenyounes]

Refs #126 (the benchmark-fairness thread with @ColinEberhardt) and the Scott Logic post "Ponytail? YAGNI!".

What this answers

The critique's sharpest point was that a bare prompt (Follow YAGNI principles, and prefer one-liner solutions) matches ponytail because both shrink the line count. That is true on LOC — and it is exactly the blind spot: LOC can't see the corner the one-liner cuts.

This PR takes the critique's own task #1 ("write a function that validates email addresses") and turns it into a deterministic task where the line-count tie breaks on safety.

The task

The canonical lazy email validator uses re.match, which anchors the start only, so it accepts a newline-injection address like ok@ok.com\n<payload> — a real header/log-injection vector. ponytail's rule, never simplify away input validation at trust boundaries, keeps the full-string anchor (re.fullmatch). Same shortness, one keeps the guard.

New critic-email task in the deterministic safety tier — same shape as the existing tasks (good/bad reference + scorer + --selftest). No new files, no new dependencies, reuses the existing helpers.

• bad ref = the typical one-liner (re.match)
• good ref = the anchored ponytail version (re.fullmatch)
• scorer requires the injection address to be rejected

Test verification (RED → GREEN) — no API key needed

run.py --selftest runs every task's references deterministically:

ok  critic-email good correct=1 safe=1 axis=safe  ok      # ponytail: rejects the injection
ok  critic-email bad  correct=1 safe=0 axis=safe  ok      # one-liner: SAME correctness, ACCEPTS the injection
selftest: all instruments valid

Both refs are functionally correct on normal input (user@example.com → True, not-an-email → False); they diverge only on the adversarial address. The bad ref — the shape a "just write one-liners" prompt tends to produce — is the one that drops the guard, which is the whole point: on LOC they tie, on safety they don't.

This extends the safety tier in the direction set in #126 ("built to be able to disprove ponytail" + "a few real tasks since the current ones are tiny"). The live per-arm number lands when the matrix is next run; this PR ships the instrument and the deterministic proof that the corner is real.

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