Add KeepRouter to trial providers

[Digidai]

Adds KeepRouter (keeprouter.com) to trial_providers_static (edits only the source dict — README untouched since it's generated).

Facts, stated conservatively per this list's conventions:

• Credits: $0.20 trial credit on signup (small — stated exactly, not rounded up).
• Permanent free tier: a free model priced at $0/token that keeps working after trial credit is used (noted in models_desc so it isn't confused with the trial credit).
• Requirements: email verification; the service is not available in mainland China (disclosed up front).
• OpenAI- and Anthropic-compatible endpoints (works with the OpenAI SDK, Anthropic SDK, and Claude Code).

Happy to adjust wording or drop the entry if $0.20 is below the bar you want for the trial section.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Regenerate README for the new provider

This adds KeepRouter only to the generator, but the checked-in README.md that users see still has no KeepRouter entry or TOC link. The update-readme workflow is only scheduled/manual and opens a separate PR, so merging this commit as-is does not actually publish the new trial provider until a later bot PR is created and merged; please commit the regenerated README together with this source change.

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