feat: add Atlas Cloud provider preset

[binyangzhu000-sudo]

Summary

• add Atlas Cloud to the engine and Web UI provider catalogs
• configure its default OpenAI-compatible endpoint, API key environment variable, and qwen/qwen3.8-max capabilities
• document YAML setup and cover both catalogs with focused tests

Validation

• pnpm exec tsx --test tests/model/config/parseModelConfig.spec.ts (8 passed)
• pnpm --dir ui exec vitest run src/shared/catalogProviders.test.ts (5 passed)
• pnpm build
• pnpm --dir ui build
• changed-file UI ESLint
• real PilotDeck runtime request through the catalog returned PILOT_ATLAS_OK

Baseline notes

• root full suite: 227 passed, 0 failed, 7 cancelled; the isolated network test has the same timer cancellations on unmodified main
• UI full suite: 606 passed, 8 failed; unmodified main has the same 8 failures (605 passed)
• UI typecheck and full lint retain existing baseline errors (496 type errors; 1 lint error and 93 warnings)