feat(faceswap): expose yaw on enumeration too

ListFaces now carries head yaw, so a caller choosing WHICH face to swap can
see the thing that decides whether the swap will read — not only learn it
afterwards from the swap report. In the run that prompted this the target's
three faces sat at -82, -8 and -11 degrees; only the first was hopeless, and
nothing in a bounding box said so.

imagegen/faceswap.go

@@ -55,6 +55,14 @@ type DetectedFace struct {
 	Box [4]int
 	// Score is the detector's confidence, 0-1.
 	Score float64
+
+	// Yaw is how far the head is turned from camera, in degrees, or nil when
+	// the provider does not report pose. Exposed on ENUMERATION, not just
+	// after the fact, because it is how a caller picks a face a swap will
+	// actually work on: past roughly ±45° the features carrying identity are
+	// edge-on, and the result reads as a generic person however good the
+	// transfer is. A bounding box cannot show this.
+	Yaw *float64
 }
 
 // Size returns the box dimensions. Derived rather than stored: carrying

provider/llamaswap/faceswap.go

@@ -46,6 +46,7 @@ type facesResponse struct {
 		Score  float64  `json:"score"`
 		Width  int      `json:"width"`
 		Height int      `json:"height"`
+		Yaw    *float64 `json:"yaw"`
 	} `json:"faces"`
 }
 
@@ -74,7 +75,7 @@ func (m *faceSwapModel) ListFaces(ctx context.Context, img imagegen.Image) ([]im
 	}
 	out := make([]imagegen.DetectedFace, 0, len(parsed.Faces))
 	for _, f := range parsed.Faces {
-		df := imagegen.DetectedFace{Index: f.Index, Score: f.Score}
+		df := imagegen.DetectedFace{Index: f.Index, Score: f.Score, Yaw: f.Yaw}
 		// A short box would silently index out of range below; treat a
 		// malformed entry as a protocol error rather than zero-filling it,
 		// because a wrong box sends the caller at the wrong face.