feat: allow passing full asset to bypass looking up asset in mux

[jsanford8]

Note

Medium Risk
Broadly changes public workflow function signatures to accept either an asset ID or a pre-fetched MuxAsset, which could break callers and alters how playback IDs/policies are resolved. Runtime risk is moderated by added unit tests covering the new branching logic.

Overview
Allows callers to pass a full MuxAsset into major workflows (e.g. getSummaryAndTags, generateChapters, askQuestions, moderation, translations, embeddings) to bypass the Mux Video API fetch when the asset is already available.

Adds toPlaybackAsset (now exported) to derive playbackId/policy directly from an asset object, updates workflows to branch on string vs MuxAsset, and introduces unit tests asserting the correct path is taken (Mux fetch vs local resolution), including extra moderation coverage.

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