TODO: emit cpp (real-time C++ backend)

Goal

Implement model-parser emit cpp that lowers IR into a deterministic, real-time-safe C++ representation for PLC / embedded targets, aligned with the existing realtime-cpp validation profile.

Why

• Second major consumer of the same IR after Julia, proving the hub-and-spoke design (one expression tree, many renderers).
• Org roadmap: trajectory or numerical parity checks against the Julia path where feasible.

Scope hints

• Constrain to profile-checked operators/functions only; reject or warn clearly.
• Pure codegen in Python; no new runtime dependency for users who only need IR or Julia.

References

• docs/design/model-parser.md roadmap §4.
• src/model_parser/validation/validators.py (profile behaviour).

Acceptance sketch

• CLI: emit cpp with -o path.
• Tests: small IR fixture and expected .cpp (or fragment) under tests/ or examples/.