feat(extraction-service): scaffold promptfoo eval suite with 19 test cases
- Add evals/promptfoo.yaml: HTTP provider hitting extraction-service API
covering all 5 built-in tasks (transcript, triage, memory-insight,
reflection-enrichment, bug-report-extraction)
- Add evals/fixtures/golden.json: machine-readable golden input/output fixtures
- Add evals/run-evals.sh: shell runner with health checks, auth token
handling, task filtering, and CI mode
- Add evals/README.md: usage docs, prerequisites, cost estimates, CI integration
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