phpperf evidence

• ph-array-merge-rebind — measured (ph-array-merge-rebind.md + ph-array-merge-rebind.jsonl); default severity error.
• ph-string-dot-hot — measured (ph-string-dot-hot.md + ph-string-dot-hot.jsonl); default stays off (G3: mostly OK-idiom).
• ph-echo-hot — measured (ph-echo-hot.md + ph-echo-hot.jsonl); default stays hint.

See ../docs/evidence-policy.md and root docs/rule-regression.md.