docs: connect Seedance media asset workflow

[sam2tom]

Summary

• add a dedicated Media Assets for Seedance guide under Official Native API
• document the complete local upload or public URL -> /v1/assets registration -> readiness lookup -> asset:// generation workflow
• map Image, Video, and Audio Assets to Seedance content item types and roles
• link Seedance 2.0, Seedance 2.5, the native API overview, and the generic Media Assets reference into one workflow
• clarify that the public Asset surface currently exposes registration and lookup, without advertising groups, listing, updates, or deletion
• add navigation and content regression coverage

Validation

• npm run validate

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-31T14:24:43.523505Z	f5a7db5	New commits

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