feat(cli): Add LiteLLM as a first-class provider

[roomote-v0]

This PR attempts to address Issue #10839 by adding LiteLLM as a first-class provider in the Roo Code CLI.

Summary

LiteLLM already has backend support in the core types package, but the CLI did not expose it as a first-class provider. This implementation updates the CLI to support LiteLLM with the following changes:

Changes

New Provider Support

• Added "litellm" to the supportedProviders array in apps/cli/src/types/types.ts
• Added litellm: "LITELLM_API_KEY" to the environment variable mapping

New CLI Flag

• Added --litellm-base-url <url> flag for specifying the LiteLLM endpoint
• Default value: http://localhost:4000 when using litellm provider

Environment Variables

• LITELLM_API_KEY - API key for LiteLLM
• LITELLM_BASE_URL - Base URL for LiteLLM endpoint (optional)

Provider Settings

Added support in getProviderSettings() for:

• litellmApiKey
• litellmModelId
• litellmBaseUrl

Documentation

Updated CLI README with LiteLLM provider documentation including:

• New --litellm-base-url option in the Options table
• LiteLLM entry in the Environment Variables table
• New LiteLLM Environment Variables section

Tests

Added tests for:

• getApiKeyFromEnv with litellm provider
• getProviderSettings with LiteLLM-specific settings

Usage Examples

# Using environment variables
export LITELLM_API_KEY="your-key"
export LITELLM_BASE_URL="http://localhost:4000"
roo --provider litellm -m claude-3-sonnet "your prompt"

# Using flags
roo --provider litellm --api-key "your-key" --litellm-base-url "http://localhost:4000" -m claude-3-sonnet "your prompt"

# Using default local LiteLLM (http://localhost:4000)
roo --provider litellm --api-key "your-key" "your prompt"

Closes #10839

Feedback and guidance are welcome!

---

Important

Add LiteLLM as a first-class provider in the CLI, updating provider settings, CLI options, and environment variables, with tests to ensure functionality.

• Provider Support:
  • Add "litellm" to supportedProviders in types.ts.
  • Map litellm: "LITELLM_API_KEY" in provider.ts.
  • Update getProviderSettings() in provider.ts to handle litellm with apiKey, model, and baseUrl.
• CLI Options:
  • Add --litellm-base-url <url> option in index.ts and run.ts.
  • Default litellmBaseUrl to http://localhost:4000 if not provided.
• Environment Variables:
  • Document LITELLM_API_KEY and LITELLM_BASE_URL in README.md.
• Tests:
  • Add tests for getApiKeyFromEnv and getProviderSettings with litellm in provider.test.ts.

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[roomote-v0]

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Review complete. No issues found.

This PR cleanly implements LiteLLM as a first-class provider with proper type safety, environment variable handling, and comprehensive test coverage.

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