dsh-plugin-llmtr: LLMTR AI Gateway Provider

The LLMTR plugin provides DeepSeek Harness with a unified AI gateway interface, enabling access to more than 170 heterogeneous models through a single API key. The plugin registers models under `ctx.llm` and supports the OpenAI-compatible protocol, Turkish localization, and inference capability display. After installation, users can set the API key, filter the model list, pin specific models, or adjust the context window in the configuration. The plugin supports chat completions and text interactions only, ensures request header privacy and security, and resolves the challenges associated with managing multi-vendor models.