feat: add Friendli provider reasoning support

[Lee-Si-Yoon]

What

Adds Friendli-specific reasoning handling to the openai-compat provider switch in coordinator.go, and adds FRIENDLI_API_KEY to the environment variables table in the README.

Friendli is being added to Catwalk in charmbracelet/catwalk#486. This PR handles the Crush-side coordinator support.

Why the separate case

Friendli's reasoning API works differently from the other openai-compat providers. Instead of reasoning_effort or thinking.type, it uses:

• chat_template_kwargs.enable_thinking to toggle reasoning on controllable models
• parse_reasoning to split reasoning into a separate reasoning_content field
• include_reasoning to include reasoning content in the response

Without this case, reasoning content would stay inline in the content field, making it harder for Crush to distinguish between thinking and answer text.

Note

The provider ID is referenced as a string literal ("friendli") rather than catwalk.InferenceProviderFriendli because the Catwalk version in go.mod predates that constant. Once Catwalk is bumped, this can be switched to the typed constant.

[charmcli]

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[Lee-Si-Yoon]

I have read the Contributor License Agreement (CLA) and hereby sign the CLA.