Organize documentation by moving requirements (HighLevelReqs, Component-*,
lmxproxy_protocol) to docs/requirements/ and test infrastructure docs to
docs/test_infra/. Updates all cross-references in README, CLAUDE.md,
infra/README, component docs, and 23 plan files.
Defines a gRPC server implementing the scada.ScadaService proto that bridges
to the existing OPC UA test server. Enables end-to-end testing of
RealLmxProxyClient without a Windows LmxProxy deployment.