Add Atlas Cloud provider preset

[binyangzhu000-sudo]

Summary

• add Atlas Cloud as a first-class OpenAI-compatible provider preset
• wire it into provider registration, default config, provider model catalog, and provider API updates
• add a focused model-catalog test for Atlas Cloud preferred chat models

Validation

• performed diff/self-review and basic brace-balance checks on changed TypeScript files
• attempted local npm install, but dependency installation stalled without output and was stopped before vitest/tsc could run

No README changes. No sponsor, logo, credits, or partner placement.