[FEATURE]: Add MTPLX to the local providers in the providers docs

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Describe the enhancement you want to request

I am Youssof, the author of MTPLX (https://github.com/youssofal/MTPLX), a local inference engine and Mac app for Apple Silicon. It serves an OpenAI-compatible API on http://127.0.0.1:8000/v1, ships mtplx start opencode, which launches OpenCode already configured, and it is the engine behind the 125 tokens per second Qwen 3.8 Flash Next runs inside OpenCode on an M5 Max (logs at https://mtplx.com/benchmarks/). The MTPLX packs on Hugging Face have 640,000 downloads.

The providers page lists the local options (Atomic Chat, llama.cpp, LM Studio, Ollama). I would like to add an MTPLX section in the same format: the opencode.json example, the served model ids, and one line per field, like the LM Studio section. The pull request is ready and references this issue.