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.

provider/llamaswap/faceswap.go

@@ -41,11 +41,12 @@ type faceSwapModel struct {
 type facesResponse struct {
 	Count int `json:"count"`
 	Faces []struct {
-		Index  int     `json:"index"`
-		Box    []int   `json:"box"`
-		Score  float64 `json:"score"`
-		Width  int     `json:"width"`
-		Height int     `json:"height"`
+		Index  int      `json:"index"`
+		Box    []int    `json:"box"`
+		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.