feat(sdk-core): add dedicated EdDSA MPCv2 BitGo GPG public key support

[Marzooqa]

Problem

1. Wrong BitGo GPG key type

eddsaMPCv2.ts was using mpcv2PublicKey from the feature flags endpoint,
which is a secp256k1 key used for ECDSA MPCv2. The EddsaMPSDkg WASM
requires an ed25519 GPG key with an X25519 encryption subkey. Passing the
wrong key type caused an immediate "Invalid Input" error from the WASM.

2. Missing GPG signing subkey

generateGPGKeyPair('ed25519') produced:
- Primary: ed25519 (sign + certify)
- Subkey: curve25519 (encrypt)

The HSM's MPS keygen verifies each party's GPG key by calling
getSigningKey() and reading key.bindingSignatures — a property that
only exists on subkeys, not the primary key. With no dedicated signing
subkey, getSigningKey() returns the primary key and bindingSignatures
is undefined, causing:

TypeError: Cannot read properties of undefined (reading 'find')
    at /home/bitgo/hsm-api/src/api/mps.js:214

Changes

New dedicated EdDSA MPCv2 key pipeline:

• bitgoPubKeys.ts — Added eddsaMpcv2 hardcoded key map (on-prem test/staging) and isBitgoEddsaMpcv2PubKey() validator
• baseTypes.ts — Added eddsaMpcv2PublicKey?: string to BitgoGPGPublicKey
• opengpgUtils.ts — getBitgoGpgPubKey() now reads bitgoEddsaMpcv2PublicKey from constants and returns it as eddsaMpcV2
• baseTSSUtils.ts — Added bitgoEddsaMpcv2PublicGpgKey field, getBitgoEddsaMpcv2PublicGpgKey() getter, wired through
  setBitgoGpgPubKey(); getBitgoGpgPubkeyBasedOnFeatureFlags() now returns { mpcv2PublicKey: Key, eddsaMpcv2PublicKey: Key | undefined }
• eddsaMPCv2.ts — Uses eddsaMpcv2PublicKey (ed25519) with fallback to bitgoEddsaMpcv2PublicGpgKey; validates against isBitgoEddsaMpcv2PubKey()

GPG key generation fix:

• opengpgUtils.ts — generateGPGKeyPair('ed25519') now passes subkeys: [{sign: true}, {sign: false}], producing a dedicated ed25519
  signing subkey. This matches the key structure used in the HSM's own test suite (hsm-api/test/mps.js)

Unrelated callers updated:

• ecdsa.ts, ecdsaMPCv2.ts — Destructure new return shape of getBitgoGpgPubkeyBasedOnFeatureFlags()

Test plan

• yarn run unit-test --scope @bitgo/sdk-core
• yarn run unit-test --scope bitgo
• EdDSA MPCv2 wallet creation completes DKG round 1 and round 2 on staging (pending WCI-220 bgms fix)
• ECDSA MPCv2 wallet creation is unaffected

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

TICKET: WCI-223

[linear]

WCI-223 Add dedicated EdDSA MPCv2 BitGo GPG public key support in SDK