Add Atlas Cloud provider preset

[binyangzhu000-sudo]

Summary

• Add Atlas Cloud as a built-in OpenAI-compatible provider preset.
• Seed the preset with https://api.atlascloud.ai/v1, API-key auth, and live-verified default models.
• Cover exact preset matching, catalog defaults, and runtime compatibility in the provider preset tests.

Tests

• git diff --check
• npx tsx --test src/__tests__/unit/provider-preset.test.ts (106 passed)
• npx tsx --test src/__tests__/unit/provider-icon-rule.test.ts (16 passed)
• npx eslint src/lib/provider-catalog.ts src/__tests__/unit/provider-preset.test.ts (passes with one existing _role warning in provider-catalog.ts)
• Atlas live /v1/models check returned 118 models and confirmed qwen/qwen3.5-flash plus deepseek-ai/deepseek-v4-pro

Notes

• npm ci is currently blocked by an upstream package-lock mismatch (@electron/windows-sign, cross-dirname, fs-extra, etc. missing from lockfile). I used npm install --package-lock=false --ignore-scripts for local dependency install and did not modify the lockfile.
• Full npm run typecheck currently fails in unrelated existing component files (src/components/ai-elements/*, DevOutputChips.tsx, UsageStatsSection.tsx), not in the changed provider catalog files.

README / marketing compliance

• No README changes
• No sponsor, logo, credits, or partner promotion added

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