fix: bind zero-amount proof signatures to challenge realm

[brendanjryan]

Summary

• bind zero-amount Tempo proof signatures to the challenge realm
• bump the proof typed-data domain version and keep client verification plus access-key recovery aligned
• add regression coverage for the new realm binding and ship a patch changeset

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/mppx@389

commit: 6074958