fix(docs): preserve x-fern-basic labels for runnable endpoints

[shubhamsinnh]

Summary

Adds regression coverage for x-fern-basic auth labels on runnable endpoint API definitions.

The existing OpenAPI fixture uses custom basic auth field names:

• project_id for the username field
• api_token for the password field

This change verifies that those labels are preserved through both:

• OpenAPI/IR to FDR conversion in @fern-api/register
• IR to Docs API definition conversion in @fern-api/docs-resolver

It also checks that the endpoint multiAuth entry points back to the same basic auth scheme, so callers rendering runnable endpoints can resolve the custom labels from authSchemes.

Notes

The runnable endpoint component itself does not appear to live in this package. If the UI still renders username / password, the remaining fix is likely in the renderer resolving endpoint auth scheme ids into apiDefinition.authSchemes.

Testing

• tsc --noEmit -p packages/cli/register/tsconfig.json
• tsc --noEmit -p packages/cli/docs-resolver/tsconfig.json
• git diff --check HEAD
• vitest --run src/ir-to-fdr-converter/__test__/openapi-from-flag.test.ts --testNamePattern "x-fern-basic" --config vitest.config.ts --reporter verbose
• vitest --run src/__test__/x-fern-basic-auth.test.ts --config vitest.config.ts --reporter verbose

The Vitest runs used a local Node 20 preload for navigator; the repo's DevBox setup pins Node 22.

[shubhamsinnh]

@amckinney could you sanity check if this is the right layer for #15956?

[claude]

Claude Code Review

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[devin-ai-integration]

✅ Devin Review: No Issues Found

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