Setup instructions for every major AI provider – US, Chinese, and local

This is one of the few places with consistent, high-quality setup instructions for essentially every major AI provider in one place — American frontier labs (OpenAI, Anthropic, Google, xAI), Chinese labs (DeepSeek, Alibaba/Qwen, Moonshot, Z.ai), aggregators (OpenRouter), fast inference providers (Groq, Cerebras, Together), and local runtimes (Ollama, LM Studio, LocalAI). This info exists elsewhere but is scattered across each vendor's docs with wildly varying quality. It also covers the common gotcha that a ChatGPT Plus / Claude Pro subscription is not an API key.