What the protocol knows about a PQSig scheme was spread over crypto (the
verifier registry and the wire size bounds) and config (an enable switch
and a fee switch). Collect it into a single pqSchemes table in
data/transactions, next to the PQSig type that is its only consumer.

crypto now holds only the stateless verifiers (PQFalcon1024, PQFalcon512,
PQEd25519). config keeps the EnablePQScheme* flags, which must stay
versioned consensus parameters, but no longer interprets them.
ErrPQSchemeNotSupported and ErrPQSchemeNotEnabled move to transactions.

The PQSig allocbounds become the max over the table. They are computed at
runtime, so a scheme's sizes may come from config/bounds. The built-in
values are unchanged.