ABC-016: MED bedrock scalar/crypto hygiene: popc64, unaligned sha256, SAN.h

01.h/SHA.h/NACL.h/OK.h/PRO.h grab-bag (2026-07-07 review): advertised-but- wrong bit helpers, an unaligned u64 read of a 1-aligned record, and support headers that don't do what they claim.

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