feat(wasm-mps): add ed25519_dkg_round0_import for MPCv1 → MPCv2 EdDSA retrofit

[Marzooqa]

Summary

• Adds ed25519_dkg_round0_import Rust function, internal generic implementation, and #[wasm_bindgen] WASM binding
• Uses KeyRefreshData::make_refresh_data_migrate to inject an existing MPCv1 additive scalar (pShare.u), aggregate public key (pShare.y), and chain code (pShare.chaincode) into the DKG protocol — enabling key re-sharing without generating a new key
• Round 1 (ed25519_dkg_round1_process) and Round 2 (ed25519_dkg_round2_process) are completely unchanged
• Adds TypeScript tests in dkg_import describe block following the existing round-by-round before + it pattern

Test plan

• it("performs round 0 import") — output has correct mps-ed25519-dkg-round1-message$ / state$ prefixes
• it("performs round 1") — output has correct mps-ed25519-dkg-round2-message$ / state$ prefixes
• it("performs round 2") — all parties agree on pk; pk === expected_pk; chaincode === chain_code
• it("signing round-trip at root path verifies against expected_pk") — both parties' signatures verify via libsodium
• it("signing round-trip at derived path m/0 produces a valid signature") — 64-byte signatures, both parties identical
• it("rejects mismatched expected_pk") — wrong pk causes protocol failure at round 2

Closes WCI-1217

🤖 Generated with Claude Code

[linear-code]

WCI-1217