Add configurable validation checkers

[MariaHov]

Summary

• Adds config-gated metrics: regex match, valid JSON, and LLM judge
• Uses a separately configured judge model for LLM scoring to avoid self-evaluation bias
• Keeps Course 1 defaults unchanged unless allowedMetricIds opts into the new checkers

Test plan

• With default config, only original Course 1 metrics appear
• Enable regex-match, valid-json, and llm-judge in session.config.json and confirm they appear in the metric picker
• Run regex and valid-json evals with known pass/fail cases
• Run LLM judge and confirm the UI shows the fixed judge model
• npm test

Made with Cursor

[coderabbitai]

Important

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 3bc255fc-526c-4d02-af09-427883262fd9

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