retinaface.cpp — Phase 3 placeholder

ggml port of RetinaFace (MobileNet 0.25× backbone) for face detection.

Status: not started. See plugins/plugin-vision/VISION_RUNTIME_MIGRATION.md ("Phase 3 plan" / "RetinaFace (face detection)") for the conversion strategy.

Replaces:

• src/face-recognition.ts SSD-MobileNet-v1 face detector (face-api.js).
• src/face-detector-mediapipe.ts BlazeFace alt path (stubbed; was onnxruntime).

Reference checkpoint: biubug6/Pytorch_Retinaface, MIT-licensed.