When a lesson has two or more uploaded videos each calls mintHlsCookie,
but all wrote to the same `cio_hls` cookie name. The last write won,
leaving every other video with a mismatched token and a 403 from the
CF Worker.
Cookie name is now `cio_hls_${assetId}` so each video owns its own
cookie. The tenant-router Worker, the Hono HLS fallback route, and the
transcripts route all read the per-asset name.
Rotimi Best
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