Initial commit: scene-actor-extraction pipeline

Source (KPN++ pipeline nodes, ArcFace embedders, SCRFD/YuNet detectors,
gallery builder), build scripts, and eval artifacts.

- external/KPN as a git submodule (gitea.tourolle.paris/dtourolle/KPN)
- ONNX models tracked via Git LFS (models/*.onnx)
- generated outputs, TensorRT engines, reference repos, and media ignored

src/nodes/face_aligner_node.hpp

@@ -0,0 +1,39 @@
+#pragma once
+#include "face_utils.hpp"
+
+#include <iostream>
+
+// ── FaceAlignerFunc ───────────────────────────────────────────────────────────
+// KPN node: applies a 5-point similarity transform to each detected face,
+// producing a 112×112 BGR crop suitable for ArcFace inference.
+//
+// Alignment uses cv::estimateAffinePartial2D (RANSAC) to fit the detected
+// landmarks to ArcFace canonical positions.  Degenerate detections (where the
+// affine fit fails) are silently dropped from the output vectors.
+
+struct FaceAlignerFunc {
+    static constexpr std::string_view label() { return "face_aligner"; }
+
+    AlignedSceneFrame operator()(SceneFrame sf) {
+        if (sf.source.eof || sf.faces.empty())
+            return {std::move(sf.source), {}, {}};
+
+        std::vector<DetectedFace> good_faces;
+        std::vector<cv::Mat>      crops;
+        good_faces.reserve(sf.faces.size());
+        crops.reserve(sf.faces.size());
+
+        for (auto& face : sf.faces) {
+            cv::Mat crop = align_face(sf.source.image, face.landmarks);
+            if (crop.empty()) {
+                std::cerr << "[face_aligner] degenerate detection skipped\n";
+                continue;
+            }
+            good_faces.push_back(face);
+            crops.push_back(std::move(crop));
+        }
+
+        return {std::move(sf.source), std::move(good_faces), std::move(crops)};
+    }
+
+};