Handle noisy wordpress.bench result output

[chubes4]

Summary

• Recover wp-codebox/bench-results/v1 JSON from successful wordpress.bench stdout when PHP/WordPress warning text is printed before or after the structured envelope.
• Preserve the non-JSON output as benchResults.diagnostics so warnings remain visible without corrupting recipe-run parsing.
• Extend recipe-bench-smoke with a fixture workload that emits warning-like HTML before valid bench JSON.

Fixes #959.

Validation

• npm run build
• npx tsx scripts/recipe-bench-smoke.ts

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Investigated the wordpress.bench recipe-run parsing path, drafted the parser fix and targeted smoke coverage, and ran validation commands. Chris remains responsible for review and merge.