Closes ADR-0164 §Open question #1. Enumerates the 8-primitive seed
registry for en_core_math_v1 (decimal-currency, currency, percentage,
fraction, time-amount, numeric, ordinal, mass-noun-token), fixes the
record schema (name/pattern/emits/extracted_fields/provenance/priority),
documents pairwise overlap precedence with rationale, and records 4
rejected temptations (rate phrases, compound entities, question stems,
compound numerics) so the ADR-0165 grammar/lexeme boundary doesn't get
relitigated by future authors.
