feat: migrate eval system to vitest-evals

[BYK]

Summary

Adds vitest-evals integration for structured, standardized eval runs.

Architecture

beforeAll (per scenario):
  1. Start isolated gateway (temp DB)
  2. Replay session turns through gateway (scripted interceptor)
  3. Run /lore:curate (distillation + curation)
  4. Backfill embeddings
  → Gateway is warmed up with Lore state

Each it() test:
  1. Send QA question through warmed-up gateway (LTM + recall tool)
  2. Get response
  3. FactualityJudge scores against reference answer

afterAll:
  Tear down gateway

New Files

• vitest.evals.config.ts — Separate Vitest config for evals (600s test timeout, 30min hook timeout, single-fork, vitest-evals reporter)
• packages/core/eval/lore-harness.ts — createHarness() wrapper around the Lore gateway with replayAndWarmup() for session replay
• packages/core/eval/cm1.eval.ts — CM-1 scenario (400K inflated) as vitest-evals tests
• packages/core/eval/mega-session.eval.ts — 2.3M mega-session as vitest-evals tests
• package.json — bun run evals script

What This Gets Us

• Vitest test runner — standard vitest run output, filtering, parallelism
• FactualityJudge — built-in LLM-as-judge (replaces custom judge.ts)
• GitHub Actions reporter — summary + annotations via vitest-evals/reporter
• Standard interface — each question is an it() test case

What Stays the Same

• Scenario definitions (scenarios/*.ts) — unchanged
• Gateway lifecycle — reused from harness.ts
• Scripted interceptor — reused
• Existing run.ts / harness.ts — coexist (can be removed later)

Tests

• 1752 pass, 0 fail (existing tests unaffected — .eval.ts only in eval config)
• Typecheck clean