Establish Go/C++ backend migration foundation with contract-compatible API, orchestration, and agent scaffolding

[Copilot]

This PR lays down the migration baseline to move backend ownership in-house: Go for REST/orchestration services and C++ for systems-level agent logic. It introduces a polyglot monorepo structure, preserves current API/socket contracts, and provides initial vertical-slice implementations for auth/policy/user/log and agent core capabilities.

• Monorepo structure for migration targets

  • Added service and agent roots:
    • services/go-api
    • services/go-master
    • agents/cpp-node-exporter
    • contracts
  • Added internal ownership/versioning policy for in-repo backend packages.

• Go API service (services/go-api)

  • Implemented route-compatible handlers for auth, user, policy, and logs.
  • Replaced external shared backend helpers with in-house modules:
    • validation/error response utilities
    • JWT signing/verification
    • password hashing/verification
    • auth/admin middleware
  • Added migration controls:
    • REST shadow forwarding toggle (ORCS_SHADOW_REST)
    • configurable legacy target (ORCS_LEGACY_API_BASE)
  • Added CORS hardening and bounded log response allocation.

• Go orchestration service (services/go-master)

  • Introduced realtime service scaffold with preserved event names/payload envelope semantics.
  • Added event contract constants aligned with existing socket flows.
  • Added migration flags for staged socket cutover behavior.

• C++ systems agent foundation (agents/cpp-node-exporter)

  • Added reusable internal libraries:
    • orcs_process (process discovery/termination)
    • orcs_telemetry (system telemetry)
    • orcs_platform (OS adapters for Linux/Windows/macOS)
  • Added agent executable skeleton and CMake/CTest project layout.

• Contract freeze artifacts (contracts)

  • Added REST contract spec (rest-api.yaml) for current endpoint surface.
  • Added socket event contract map (socket-events.json) to preserve event compatibility.

// in-house auth middleware replacing external shared package usage
mux.HandleFunc("/policy/setPolicy", h.requireAdmin(h.setPolicy))
mux.HandleFunc("/policy/updatePolicy", h.requireAdmin(h.updatePolicy))