[codex] Remove no-op config keys

[vnedyalk0v]

Summary

• Remove config keys that were accepted by schema/defaults but never read at runtime.
• Keep docs, defaults, schema, and TypeScript config types aligned.
• Replace two JSON stringify/parse clones in review-comment validators with structuredClone.

Changed files

• config/README.md
• config/default.codeflow.json
• docs/CONFIGURATION.md
• schemas/codeflow.schema.json
• src/config/codeflow-config.ts
• src/review-comments/review-fix-validation.ts
• src/review-comments/review-thread-triage-validation.ts
• tests/config/validate-config.test.ts

Verification

• npm run check passed: JSON, text safety, docs format, typecheck, and Vitest.
• Vitest result: 63 test files, 514 tests passed.
• git diff --check passed.

Self-review notes

• Scope is limited to the two 100% validated findings from the ponytail audit follow-up.
• Removed config keys are now rejected as additionalProperties by schema validation.
• Existing behavior for needs_human, emergency reason guidance, and GitHub GraphQL review-thread handling remains hard-coded where it already was.

Related issues and PRs

• Related issue: none provided.
• Review comments addressed: none.

Known risks or follow-up

• This is a schema/config cleanup and is breaking for existing .pi/codeflow.json files that still include the removed no-op keys.