0.12.5

## Security fix

Remove `litellm` from core dependencies in response to the litellm supply chain attack (versions 1.82.7 & 1.82.8 backdoored on March 24, 2026).

- `pip install browser-use` no longer installs litellm
- `ChatLiteLLM` wrapper is preserved — install litellm separately if needed: `pip install litellm`

See: https://github.com/browser-use/browser-use/pull/4515