#8232: Nebius token factory Provider support

# Add Nebius TokenFactory provider ## What/Why - Add Nebius as an OpenAI-compatible provider with auth choice, onboarding flows, and implicit provider auto-discovery via /models. - Add docs page for Nebius Token Fac tory and link it from provider indexes. - Nebius now appears in provider lists and can auto-load models when NEBIUS_API_KEY is set. ## Testing test <img width="912" height="218" alt="image" src="https://github.com/user-attachments/assets/cd8d528f-2556-4975-8779-de8af5928368" /> lint <img width="602" height="130" alt="image" src="https://github.com/user-attachments/assets/e527fc5e-e830-4df2-b666-4d7048cf3040" /> <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds Nebius Token Factory as an OpenAI-compatible provider across docs and onboarding flows. It introduces a new `nebius-token-factory-api-key` auth choice, stores credentials in an auth profile, applies provider config + default model wiring, and adds implicit provider auto-discovery by calling `GET /models` when a Nebius key is present. Key integration points are: - Env-key resolution (`NEBIUS_TOKEN_FACTORY` preferred, `NEBIUS_API_KEY` fallback) - Interactive + non-interactive onboarding support - Implicit provider creation in `resolveImplicitProviders` with model discovery/default fallback Main issues to address are consistency between interactive vs non-interactive env var detection, and ensuring that the “apiKey” value stored in generated config (often a source/reference string) is never treated as a literal credential by runtime call sites. <h3>Confidence Score: 4/5</h3> - This PR is mostly safe to merge; main risk is a config/env-var inconsistency that can break non-interactive onboarding in some environments. - Changes are additive and scoped to a new provider. The notable correctness concern is that non-interactive onboarding only checks `NEBIUS_TOKEN_FACTORY` while other paths accept `NEBIUS_API_KEY` as fallback, which can cause surprising failures. A secondary concern is making sure placeholder apiKey references aren’t used as real credentials by downstream code. - src/commands/onboard-non-interactive/local/auth-choice.ts, src/agents/models-config.providers.ts <!-- greptile_other_comments_section --> <!-- /greptile_comment -->