test(express): end-to-end tests for address/derive endpoint

[rajangarg047]

Summary

End-to-end tests for POST /api/v2/{coin}/address/derive that exercise the real coin derivation through the HTTP endpoint — no mocks. (The unit tests in deriveAddress.ts stub coin.deriveAddress; these don't.)

For each Phase 1 wallet kind, the test asserts the endpoint returns the exact known-good address, and that the endpoint-derived address round-trips through isWalletAddress:

• SOL (EdDSA MPC): exact address + derive→verify round-trip
• ETH (secp256k1 MPC): exact address; legacy forwarder versions (1/2/4) surface as a 500 (Stage C not yet implemented)
• BTC (UTXO multisig): exact legacy P2SH (34TTD5…) + bech32 P2WSH (bc1qjpz…) + round-trip

Context

WCN-918, rescoped: per-coin derivation + derive→verify round-trips already shipped as unit tests within the coin PRs (#9016/#9017/#9018) and the endpoint codec/integration tests shipped with the endpoint (#9013). The only genuine gap was an end-to-end test that drives real derivation through the live endpoint rather than a mocked coin — that's what this adds. Stage C (ETH forwarder, WCN-932) tests will follow with that implementation.

All Phase 1 derivation (WCN-912–917, 914) is merged to master.

Test plan

• 7 e2e tests pass (BITGOJS_TEST_PASSWORD=test mocha)
• eslint clean (prettier-formatted)
• CI

🤖 Generated with Claude Code

[linear-code]

WCN-918

[rajangarg047]

Closing — this introduced an end-to-end test pattern that doesn't exist anywhere else in the repo (real cross-package coin derivation through the endpoint, coupling the express test to the built dist of 6 packages). The repo convention is to mock the coin at the route layer.

The coverage is already in place idiomatically: real derivation + derive→verify round-trips are unit-tested in each coin package (#9016/#9017/#9018), and the endpoint wiring/validation is covered by the mocked integration test in #9013. WCN-918 is resolved as covered by those.