feat(orient): auto-orient the largest overhang toward the cooling fan

New printer option fan_direction (undefine/left/right/both, default
undefine) declares which side the auxiliary part-cooling airflow comes
from. When set and the printer has an auxiliary fan, auto-orient adds a
yaw rotation so the dominant overhang area faces the airflow, and newly
added primitive shapes are pre-oriented the same way (except the Cube,
whose axis-aligned bounding box the pressure-advance pattern calibration
depends on).

- FanDirection enum + fan_direction printer option (Accessory group,
  enabled only with auxiliary_fan)
- orient engine: weighted overhang areas per candidate, yaw-direction
  search, vertical rotation applied on top of the primary orientation;
  the cooling weights are taken from the candidate actually chosen,
  including the flat-bottom tie-break
- orient_for_cooling() for primitive placement
- set fan_direction=left on H2C/H2D/H2D Pro/X1/X1E/P1S 0.4 profiles
  (X1C/H2S/P2S/X2D/Qidi X-Max 4 already carried the key, which now
  takes effect)

With fan_direction unset or no auxiliary fan the vertical rotation stays
identity and auto-orient results are unchanged; slicing and g-code are
never affected.

src/libslic3r/Orient.hpp

@@ -26,10 +26,18 @@ struct OrientMesh {
     TriangleMesh mesh;              /// The real mesh data
     double overhang_angle = 30;
     double angle{ 0 };
+    double angle_vertical{ 0 };
     Vec3d axis{ 0,0,1 };
+    Vec3d axis_vertical{ 0,0,1 };
     Vec3d orientation{ 0,0,1 };
-    Matrix3d rotation_matrix;
-    Vec3d euler_angles;
+    Vec3d orientation_vertical{ -1,0,0 };
+    Matrix3d rotation_matrix = Matrix3d::Identity();
+    Matrix3d rotation_matrix_vertical = Matrix3d::Identity();
+    Vec3d euler_angles = {0, 0, 0};
+    Vec3d euler_angles_vertical = {0, 0, 0};
+    Vec3d cooling_direction = {0, 0, 0};
+    bool has_cooling_fan{false};
+
     std::string name;
 
     /// Optional setter function which can store arbitrary data in its closure
@@ -154,6 +162,9 @@ void orient(ModelObject* obj);
 
 void orient(ModelInstance* instance);
 
+// rotate z axis for cooling
+void orient_for_cooling(TriangleMesh& mesh, const FanDirection& fan_dir);
+
 }} // namespace Slic3r::orientment
 
 #endif // MODELORIENT_HPP