feat: add Together AI integration and provider implementation guide

- Create detailed provider implementation guide with:
  - Architecture overview and implementation steps
  - Configuration patterns and best practices
  - Testing checklist and Docker integration guide
  - Example using Together AI implementation
- Add Together AI as new provider with:
  - Environment variables and Docker configuration
  - Support for Qwen, Llama, and Mixtral models
  - API key and base URL management
  - OpenAI-compatible API integration

worker-configuration.d.ts

@@ -7,6 +7,8 @@ interface Env {
   OLLAMA_API_BASE_URL: string;
   OPENAI_LIKE_API_KEY: string;
   OPENAI_LIKE_API_BASE_URL: string;
+  TOGETHER_API_KEY: string;
+  TOGETHER_API_BASE_URL: string;
   DEEPSEEK_API_KEY: string;
   LMSTUDIO_API_BASE_URL: string;
   GOOGLE_GENERATIVE_AI_API_KEY: string;