test(promptfoo): add oracle export gate

[christso]

Summary

• add Promptfoo defaults export lowering: defaults.provider -> defaultTest.providers, defaults.grader -> defaultTest.options.provider
• add a deterministic AgentV fixture that exports to Promptfoo and executes with real promptfoo@0.121.15 eval
• assert Promptfoo JSONL matrix/provider/assertion outcomes for default provider, test options.provider, and assertion-level provider selection

Promptfoo oracle

• CLI oracle: bunx promptfoo@0.121.15 eval
• Local reference clone checked: /home/entity/projects/promptfoo/promptfoo at 6bfc5a0c7f16f9c4717ac731d276b578e63d0769
• The gate proves the exported config is accepted by Promptfoo and that Promptfoo itself executes the expected target-provider matrix and grader-provider precedence.

Validation

• bun run validate:promptfoo-export
• bunx biome check .github/workflows/ci.yml scripts/export-promptfoo-config.ts scripts/export-promptfoo-config.test.ts scripts/fixtures/promptfoo-export/oracle-matrix.agentv.yaml scripts/fixtures/promptfoo-export/oracle-target-provider.cjs scripts/fixtures/promptfoo-export/oracle-grader-provider.cjs
• tmp=$(mktemp -d); bun scripts/export-promptfoo-config.ts --input scripts/fixtures/promptfoo-export/host-environment.agentv.yaml --output "$tmp/promptfooconfig.yaml" && bunx promptfoo@0.121.15 validate config -c "$tmp/promptfooconfig.yaml"

Notes

• This stays narrow to exporter/CI behavior and does not duplicate PR fix(grader): select grader providers from shared pool #1718 or Add provider-local environment overlays #1719 runtime changes.
• Docker environment export remains explicitly rejected by the existing boundary fixture.

Bead: av-rr0r

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