feat(awm): add EdDSA MPCv2 key generation handler, types and route

[Marzooqa]

What

• Add a single AWM handler (src/advancedWalletManager/handlers/eddsaMPCV2WalletGeneration.ts) with a shareType switch matching the ecdsaEddsaSignTransaction pattern
• Add one route POST /api/{coin}/eddsampcv2/keygen/{shareType} (v1.eddsampcv2.keygen) with per-share request/response codecs in advancedWalletManagerApiSpec.ts
• Add handler tests

Handler behavior

• initialize: generates an ed25519 GPG keypair and a data key; returns the GPG public key, the data-key-encrypted GPG private key and the encrypted data key
• round1 / round2 / finalize: decrypt the data key and delegate to EddsaMPCv2Utils.createOfflineKeyGenRound{1,2}Share / createOfflineKeyGenFinalizeShare, passing partyId derived from source on every round (required by the SDK's validateAdata session binding)
• finalize also stores the key share via the key provider postKey and returns { commonKeychain, source }
• Per-share required-field validation rejects with 400

Why

• WCI-892 of the EdDSA MPCv2 external-signer key generation plan (WCI-888): AWM handlers are thin wrappers that only do key-provider encrypt/decrypt and delegate to the SDK methods

Dependencies

• Stacked on the beta bump PR (bump-versions-2026-10-12) because the SDK offline key generation methods only exist in @bitgo-beta/sdk-core ≥ 8.2.1-beta.2107. This PR's diff against the bump branch is exactly the three new-code files. Retarget to master once the bump merges.

Test plan

• initialize returns a GPG public key, the data-key-encrypted GPG private key and the encrypted data key
• round1 delegates to createOfflineKeyGenRound1Share with the source-derived partyId (USER and BACKUP both covered)
• round2 delegates to createOfflineKeyGenRound2Share with the round-1 session and both round-1 messages
• finalize delegates to createOfflineKeyGenFinalizeShare and stores the key share via postKey with { coin, source, pub, prv, type: 'tss' }
• Rejects unsupported share types and missing required fields with 400
• Full AWM test suite against the bumped SDK: 446 passing, 0 failing
• ESLint clean on changed files

Ticket: WCI-892

[linear-code]

WCI-892