feat(video): add Atlas Cloud provider

[binyangzhu000-sudo]

Summary

• add Atlas Cloud as a first-class BYO video provider
• submit and poll Atlas media generation tasks, then validate and save the returned MP4
• support text-to-video and optional first-frame image input with provider-focused tests

Configuration

Set video.provider to atlas and provide video.api_key, or use the existing OVS_VIDEO_* environment variables. The default endpoint is https://api.atlascloud.ai/api/v1 and the default model is bytedance/seedance-2.0/text-to-video.

Verification

• pnpm vitest run packages/tools/test/gen.test.ts (19 passed)
• pnpm build
• pnpm typecheck
• pnpm test (209 passed, 17 skipped by existing environment gates)
• confirmed the default model is present in the live Atlas Cloud model catalog