v2.0.0

Structured creators

get_item/search_items/list_trash/create_item/update_item's
creators field was a single flattened "Fornavn Efternavn, ..."
string. That discarded each creator's creatorType (author vs. editor
vs. seriesEditor vs. translator vs. contributor) and the
firstName/lastName vs. single-field name (institutions) distinction --
already leading to a real misread, where a proceedings' editors were
parsed as co-authors.

creators is now a list of {creatorType, firstName, lastName} (or
{creatorType, name} for single-field/institutional creators) entries --
the same shape create_item/update_item already accepted as input, so
a result from get_item/search_items can be passed straight back into
an update_item call.

Breaking change: creators's type changes from str to list[dict]
across all five tools built on the shared item summary. No
backward-compat shim -- any client parsing the old comma-joined string
needs updating to read the structured entries instead.