Add built-in LLMTR (Turkey-hosted, OpenAI-compatible) gateway provider

[knowhycodata]

Summary

Add LLMTR as a built-in provider. LLMTR is a Turkey-hosted, OpenAI-compatible AI gateway that fronts 200+ models — global providers (GPT, Claude, Gemini, Mistral, xAI) plus Turkey-hosted models with a data-residency guarantee (Trendyol Asure, Muse Glimmer, Gemma, Qwen, etc.) — behind a single /v1/chat/completions endpoint.

Why

• Gives users (especially those needing Turkey data residency) first-class access to a large model catalog without manual openai-compatible config.
• Fits the existing gateway pattern perfectly (openrouter/nvidia/zenmux), so the integration is small and low-risk.

Proposed integration

• New llmtr provider plugin injecting an @ai-sdk/openai-compatible provider into the catalog at https://llmtr.com/v1.
• New llmtr integration with API-key + env (LLMTR_API_KEY) auth; bearer key resolves through the standard credential path.
• Live model discovery from the public /v1/models endpoint (OpenRouter-style schema: per-token pricing → per-1M cost, modalities, tool support, context limits), with a curated offline seed of Turkey-hosted flagships. LLMTR_BASE_URL overrides the endpoint.

Auth / usage

pentestcode auth login    # pick "LLMTR", paste API key
# or
export LLMTR_API_KEY=sk-...

PR implementing this follows.