feat(cli): route AI example enhancement through FAI

[kafkas]

Description

Linear ticket: Closes FER-11465

Repoints CLI AI example enhancement from fdr-lambda-docs to the new FAI /examples/enhance endpoint.

This is the CLI-side follow-up to the FAI backend change. The CLI now sends enhancement requests to FAI in dev and prod, while preserving the existing payload shape, Venus JWT auth flow, retry behavior, timeout handling, and fallback-to-original-example behavior.

Changes Made

• Renamed the AI example enhancement client from lambda terminology to FAI terminology (lambdaClient.ts -> faiClient.ts, LambdaExampleEnhancer -> FaiExampleEnhancer, DEFAULT_FDR_LAMBDA_DOCS_ORIGIN -> DEFAULT_FAI_ORIGIN).
• Updated the enhancement request path from /v2/registry/ai/enhance-example to FAI's /examples/enhance.
• Pointed dev CLI builds at https://fai-dev2.buildwithfern.com and prod CLI builds at https://fai.buildwithfern.com, matching each build's Venus environment.
• Cleaned up obsolete lambda wording in logs, errors, comments, and tests.

Testing

• Unit tests added/updated
• Manual testing completed

Manual testing:

• Rebuilt the dev CLI and published a test docs site using fai-dev2.
• Rebuilt the prod CLI and published a test docs site using prod FAI.
• Verified the CLI minted Venus JWTs, called FAI, generated enhanced examples, wrote ai_examples_override.yml, and published the docs site successfully.
• Verified prod steady-state behavior with a second prod run: 7/7 endpoints enhanced on the first attempt, no retries/timeouts, and the site published successfully.

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[devin-ai-integration]

Devin Review found 1 potential issue.