Implement FROST DKG coordinator

[mswilkison]

Summary

• add FROST WalletRegistry and FrostDkgValidator bindings plus config and chain attachment
• implement v4 FROST DKG result digest assembly with full vs active member types and fixture-backed parity tests
• add the native FROST DKG engine boundary, P2P round protocol, result signing, coordinator lifecycle, challenge monitoring, and wallet ID handling for x-only output keys

Notes

• Stacked on FROST/ROAST readiness branch #3866 / feat/frost-schnorr-migration-scaffold.
• Runtime DKG still requires the concrete native DKG engine registration from the frost-uniffi-sdk UDL/Rust export work.

Validation

• go test ./pkg/chain/ethereum ./pkg/chain/ethereum/frost/gen/... ./pkg/frost/registry ./pkg/frost/signing ./config ./cmd
• go test ./pkg/tbtc
• go test -tags "frost_native frost_tbtc_signer" ./pkg/frost/signing ./pkg/tbtc -run "TestExecuteNativeFROSTDKG|TestUniFFINativeFROSTDKGEngine|TestNativeFROSTDKGResultSignerMaterial|TestCalculateWalletIDForSigner|TestNonExistentFrostCompileOnly"
• env KEEP_CORE_FROST_TBTC_SIGNER_ACCEPT_SCAFFOLD_KEY_GROUP=true go test -tags "frost_native frost_tbtc_signer" ./pkg/tbtc