Vertex AI Multi-Provider CLI — Claude, Gemini, Grok

Vertex AI Model Garden exposes third-party models (Anthropic, xAI, Meta, Mistral, DeepSeek) through a single OpenAI-compatible chat-completions API. This CLI abstracts away gcloud auth, project IDs, and JSON request construction so you can chat with any model in one line. Features: auto-fetches access tokens via gcloud and caches until expiry, reads project ID from a central ~/keys file, accepts prompts as argument, STDIN, or via -p flag (pipe-friendly), clean error messages instead of curl noise. Built as a single dependency-free Bash script using curl + jq, deployable to Termux, Linux, or macOS in under a minute.