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.
• The digest fixture now records the tBTC TypeScript generator source and regeneration command. A paired tBTC PR should still commit the mirror fixture at docs/test-vectors/frost-dkg-result-digest-v1.json and add the TS-side emitter/test; until then, the keep-core test verifies the pinned bytes and metadata but does not compare against a checked-in tBTC mirror file.

Validation

• go test ./pkg/frost/registry ./pkg/chain/ethereum ./pkg/chain/ethereum/frost/gen/...
• go test ./pkg/tbtc -run "TestFrostDKGSignatureThreshold|TestBoundedFrostDKGRecoveryStartBlock|TestFrostDKGRecoveryLookBackBlocks" -count=1
• go test -tags "frost_native frost_tbtc_signer" ./pkg/tbtc -run "TestLowestLocalActiveMemberIndex|TestFrostMisbehavedMemberIndices|TestFrostDKGSignatureThreshold|TestBoundedFrostDKGRecoveryStartBlock|TestFrostDKGRecoveryLookBackBlocks" -count=1
• CI client-build-test-publish passes on the prior pushed commit; rerunning for the latest follow-up commit after push.

Local Note

• Full local go test ./pkg/tbtc currently fails in standalone TestWatchCoordinationWindows; this reproduces when run by itself and appears unrelated to the FROST DKG coordinator changes.