Sharding required a 32-hex UUID and threw "Invalid UUID format" on every
non-UUID id, even though add()'s own docs show `id: "user-12345"` and the u64
id-mapper happily assigns ints to any string. So custom ids mapped fine in
memory then threw on save — breaking documented usage and any 7.x consumer
using friendly ids (`'user-123'`, slugs, emails) on upgrade.
getShardId() (renamed from getShardIdFromUuid) now buckets UUID-format ids by
their first byte (on-disk layout unchanged, so existing data never moves) and
hashes any other id via FNV-1a into the same 256-bucket space. The hash is part
of the on-disk contract and must not change. Verbs stay Brainy-generated UUIDs
by contract; only custom noun ids take the hash path.
Adds getShardId unit coverage: dual scheme, determinism, even distribution
across buckets, and the empty-id guard.
