Add additional breakdown for "claims in channel" metadata

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Adding a breakdown by claim type and stream types would be useful for apps that want to show certain attributes of the channel without having to claim search multiple times.

For instance, when I load a channel page, I want to know if the channel has playlists. To do this today, need to claim search with the claim type collection after resolving.

Another example: we may want to add a tab for posts - today we'd need to claim search with stream type = document.

The other use case would be something like showing a tab for shorts - this one is trickier as there's no great way to identify shorts, but we could do something via a tag: #shorts. So maybe we'd also add a breakdown of how many times a tag appears across a channel?

Start by tracing the channel metadata and claim-search flow described in the issue, including claim type, stream type, and tag handling. Define the requested breakdowns for playlists, posts, shorts, and tags, then verify that the resulting metadata supports these channel-page use cases without repeated searches.

Written by the indexing model from the issue text.