feat(providers): Z.ai Start Plan provider (OAuth login, in-process traceless captcha, gateway wire) - #4647

PR hygiene failed: new_suppression, unsponsored_surface

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/