Add SDK version compatibility check via header

[bitcoin-coder-bob]

Clients (SDKs) currently have no way to signal which arkd server version they were built against. When the server introduces breaking changes to an endpoint (e.g., request/response format changes), clients silently get wrong behavior or cryptic errors.

Add a version compatibility check so the server can proactively reject outdated clients with a clear, structured error telling them to update.

support both grpc and rest

[bitcoin-coder-bob]

working off PR: #960