Add PZERO OpenAI-compatible provider

Please add PZERO as an OpenAI-compatible provider so OpenCode /connect can list it without a paste-only custom provider.

PZERO is prepaid inference (chat, image, video) at https://api.pzero.studio/v1. Auth env: PZERO_API_KEY (keys are pzero_…). Live catalog: GET https://api.pzero.studio/v1/models (public). Docs: https://docs.pzero.studio/agents/quickstart. Conversion door: https://pzero.studio/agents

Suggested providers/pzero/provider.toml:

name = "PZERO"
npm = "@ai-sdk/openai-compatible"
api = "https://api.pzero.studio/v1"
env = ["PZERO_API_KEY"]
doc = "https://docs.pzero.studio/agents/quickstart"

I cannot open the PR from this account (no public fork). Happy to supply model.toml files from the live text catalog if a maintainer wants a first slice (for example deepseek-v4-flash). Sign-in is free; usage is paid (min 1 USDC on Base). No starter credits.

Start with the proposed providers/pzero/provider.toml and compare it with neighboring provider definitions. Add the PZERO endpoint, environment variable, package, and documentation URL, then verify that PZERO appears in OpenCode /connect and can load its public model catalog.