fix(review-pr): remove unsupported schema patterns

[Sayt-0]

Summary

• remove JSON Schema pattern constraints rejected by the Docker models gateway from the drafter and verifier structured outputs
• preserve minLength: 1 and enforce whitespace-only or placeholder refusal output through fail-closed orchestration checks
• update regression tests to pin the provider-minimal schemas and semantic refusal handling

Root cause

The models gateway rejected the structured-output schema before sub-agent execution:

• the original bounded regex failed with Cannot apply a range quantifier
• a simplified regex still failed with Schema is too complex

This caused transfer_task to fail and reviews to be posted as incomplete.

Validation

Check	Result
Exact drafter schema through models gateway	pass
Exact verifier schema through models gateway	pass
End-to-end review eval	pass, 6/6 relevance criteria
Unit tests	pass, 933 tests
TypeScript typecheck	pass
Biome	pass
Build	pass
actionlint	pass
Fresh-eyes review	approved

Changed files

• review-pr/agents/pr-review.yaml
• src/pr-review-agent/__tests__/pr-review-yaml.test.ts