collection_types field with list of all claim/stream-types contained in the collection

Edit: This has to be done at lookup time in case streams associated with claims change.

It would be handy to enforce collection_type s such as 'mixed', 'channels', 'playables', 'photos', etc. because

1. then they can be displayed and filtered by type,
2. a 'channel list' can be made to only include channels, etc. and
3. so that less logic is required to route a collection to its proper display,
4. we don't have to get and inspect every claim to be sure what the type intention was (initially, we load the first (5) claim items).
5. it's impossible to know whether the intent is for a mixed list.

Alternative to having a type field:
Collections are anything-goes. Collections created on one device force a guess as to the intentions when pulled to another device OR the entire list must be inspected claim by claim.

The issue names no files, tests, or entry points. Start by locating collection lookup and the collection data model, then clarify how claim and stream types should be derived when associations change; done means the lookup exposes the agreed type information without relying on a partial claim list.