docs(openrouter): add documentation for OpenRouter API (#3705)

* docs(openrouter): add documentation for OpenRouter API and supported models

* docs(openrouter): remove outdated model list from OpenRouter API documentation

Author: Sma1lboy

website/docs/references/models-http-api/openrouter.md

@@ -0,0 +1,27 @@
+# OpenRouter
+
+[OpenRouter](https://openrouter.ai/) provides unified access to multiple AI models through an OpenAI API compatible RESTful endpoint, including models from OpenAI, Anthropic, Google, and Meta.
+
+## Chat Model
+
+OpenRouter provides an OpenAI-compatible chat API interface.
+
+```toml title="~/.tabby/config.toml"
+[model.chat.http]
+kind = "openai/chat"
+model_name = "openai/gpt-4"  # Can be any model from https://openrouter.ai/models
+api_endpoint = "https://openrouter.ai/api/v1"
+api_key = "your-api-key"
+```
+
+## Completion Model
+
+OpenRouter does not offer completion models (FIM) through their API.
+
+## Embeddings Model
+
+OpenRouter does not offer embeddings models through their API.
+
+## Supported Models
+
+For a complete list of supported models, visit [OpenRouter's Model List](https://openrouter.ai/models).