fix(hermes): reject review as a default mode

[Iams4kura]

Summary

• Fixes: With PONYTAIL_DEFAULT_MODE=review or defaultMode set to review, every Hermes LLM call receives the review-only ruleset instead of falling back to the full runtime mode.
• Root cause: Hermes _default_mode validates persistent defaults with _normalize_config_mode, whose domain intentionally includes the explicit session-only review mode, rather than _normalize_runtime_mode.

Regression evidence

• Before: node --test tests/hermes-plugin.test.js exited 1

• After: node --test tests/hermes-plugin.test.js exited 0

Verification

• npm test
• node scripts/check-rule-copies.js
• node scripts/check-versions.js
• python3 -m py_compile __init__.py
• git diff --check

Scope

• 2 files changed, +27 / -2 lines

Authorship

This fix was developed with AI assistance and was validated with the regression and project checks listed above.