docs(proxy): document LITELLM_CORS_EXPOSE_HEADERS env var

[devin-ai-integration]

Summary

Documents the new LITELLM_CORS_EXPOSE_HEADERS env var in the proxy environment variables reference, alongside the existing LITELLM_CORS_ORIGINS / LITELLM_CORS_ALLOW_CREDENTIALS entries. The var lets operators expose additional x-litellm-* response headers via Access-Control-Expose-Headers so browser clients calling the proxy cross-origin can read them (e.g. x-litellm-response-cost, x-litellm-model-api-base)

Pairs with the code change in BerriAI/litellm#33125. The litellm repo's documentation validation CI checks out this docs repo and asserts every os.getenv(...) key is documented in config_settings.md, so that check stays red until this merges

Link to Devin session: https://app.devin.ai/sessions/4db978bbfa1045a8a89c634e6648eeba

[devin-ai-integration]

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Jul 13, 2026 10:18pm