fix(realunit): accept registration signatures over a chainId-extended EIP-712 domain

[Blume1977]

Problem

BitBox users cannot complete the RealUnit registration: on submit, the BitBox02 (Nova) rejects the signing request with "typed data has no chain ID" shown on the device. The firmware requires a chainId in the EIP712Domain, but both the app's signing payload and our verification use the chainId-less domain { name: 'RealUnitUser', version: '1' }. Software wallets sign the payload regardless, which is why this never surfaced before. First affected customer: userData 412822 (23.07.).

Change

resolveSignedRegistrationMessage now accepts signatures over both domain variants:

• legacy: { name, version } (all existing registrations, software wallets)
• chainId-extended: { name, version, chainId } with the REALU token chain (Ethereum on PRD, Sepolia on DEV/LOC — same value the app receives as apiConfig.asset.chainId)

Verification loops domains inside the existing UTF-8/ASCII transliteration loop. No DTO or forward-payload change.

Pair PR / merge order

1. This PR first (backward compatible, safe alone — accepts strictly more).
2. App PR (RealUnitCH/app): hardware wallets sign with the chainId-extended domain; software wallets stay on the legacy domain to avoid any risk with Aktionariat's re-verification of existing flows.

Open coordination point (blocking for the app rollout, not for this PR)

Aktionariat re-verifies the registration signature against the payload we forward. If their verification is pinned to the legacy domain, chainId-signed (BitBox) registrations will fail on their side as "Invalid signature" at forward time. This must be confirmed with Aktionariat (structured question via Dani) before the app change ships — the new test documents this dependency explicitly.

Tests

• accepts a BitBox signature over the chainId-extended domain and forwards the signed ASCII fields (incl. proof that legacy-domain recovery does NOT match → Aktionariat dependency documented)
• rejects a signature over a foreign chainId
• all existing signature/transliteration tests unchanged: 332/332 green

[github-actions]

⚠️ Unverified Commits (1)

The following commits are not signed/verified:

• 6fa43cf fix(realunit): accept registration signatures over a chainId-extended EIP-712 domain (Blume1977)

How to sign commits

# SSH signing (recommended)
git config --global gpg.format ssh
git config --global user.signingkey ~/.ssh/id_ed25519.pub
git config --global commit.gpgsign true

# Re-sign last commit
git commit --amend -S --no-edit
git push --force-with-lease