feat: add LiteLLM as LLM provider (Python SDK + TypeScript proxy)

[RheagalFire]

Summary

Add LiteLLM as an LLM provider, giving users access to 100+ LLM providers (OpenAI, Anthropic, Google, Azure, AWS Bedrock, Ollama, Cohere, Mistral, and more) through a single unified interface. Python SDK uses the native litellm SDK (litellm.acompletion); TypeScript SDK uses LiteLLM as an OpenAI-compatible proxy.

Changes

• libraries/python/getpatter/providers/litellm_llm.py - LiteLLMProvider satisfying the LLMProvider protocol (streaming, tool calls, cancel_event barge-in, usage tracking, warmup). drop_params=True by default for cross-provider compatibility.
• libraries/python/getpatter/llm/litellm.py - thin LLM wrapper with LITELLM_API_KEY env var fallback.
• libraries/typescript/src/llm/litellm.ts - LLM preset extending OpenAICompatibleLLMProvider with LiteLLM proxy defaults (LITELLM_BASE_URL, LITELLM_API_KEY).
• libraries/python/pyproject.toml - litellm = ["litellm>=1.80.0,<2.0"] optional extra.
• libraries/python/tests/test_litellm_llm.py - 7 unit tests (mocked).
• libraries/typescript/tests/litellm-llm.test.ts - 4 unit tests.
• Registration in both SDK barrels (__init__.py, index.ts) with LiteLLMLLM flat alias and litellm namespace object.

Pre-merge checklist

• Local validation is green: bash scripts/pr-validate.sh (mirrors the
  PR-blocking CI — Python + TypeScript tests, lint, pre-commit).
• Both SDKs updated when the change is user-visible — every public
  feature ships in Python AND TypeScript in the same PR, same API shape
  and defaults (snake_case ↔ camelCase). New/Python-only or TS-only is
  not accepted.
• CHANGELOG.md updated — added an entry under ## Unreleased
  (### Added / ### Changed / ### Fixed / …) for any user-visible
  change. Refactor / test-only / docs-only diffs are exempt — say so below.
• Tests added for new behaviour; only the paid/external boundary
  (carrier / provider WebSocket) is mocked.
• No secrets, credentials, or real phone numbers / PII in the diff.
• No external license headers or "ported from " provenance
  comments in source files (integrating a provider/carrier and naming it
  is fine; copying a competitor's lineage is not).

Breaking change?

No — or describe the migration path.