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/slic3r/GUI/GUI_ObjectList.cpp

@@ -38,6 +38,7 @@
 
 #include "slic3r/Utils/FixModelByCgal.hpp"
 #include "libslic3r/Format/bbs_3mf.hpp"
+#include "libslic3r/Orient.hpp"
 #include "libslic3r/PrintConfig.hpp"
 
 #ifdef __WXMSW__
@@ -2560,6 +2561,15 @@ void ObjectList::load_shape_object(const std::string &type_name)
     // Create mesh
     BoundingBoxf3 bb;
     TriangleMesh mesh = create_mesh(type_name, bb);
+    // Rotate the largest overhang area toward the part cooling fan so new shapes start in a
+    // cooling friendly orientation. Skip the plain cube: the pressure advance pattern
+    // calibration reuses it as an axis-aligned anchor and scales it by its bounding box,
+    // so its orientation must stay fixed.
+    const Slic3r::DynamicPrintConfig& full_config = wxGetApp().preset_bundle->full_config();
+    if (type_name != "Cube" && full_config.has("fan_direction") && full_config.has("auxiliary_fan")) {
+        FanDirection config_dir = full_config.option<ConfigOptionEnum<FanDirection>>("fan_direction")->value;
+        orientation::orient_for_cooling(mesh, config_dir);
+    }
     // BBS: remove "Shape" prefix
     load_mesh_object(mesh, _(type_name));
     wxGetApp().mainframe->update_title();

src/slic3r/GUI/Jobs/OrientJob.cpp

@@ -229,15 +229,32 @@ orientation::OrientMesh OrientJob::get_orient_mesh(ModelInstance* instance)
     auto obj = instance->get_object();
     om.name = obj->name;
     om.mesh = obj->mesh(); // don't know the difference to obj->raw_mesh(). Both seem OK
+    const Slic3r::DynamicPrintConfig& config = wxGetApp().preset_bundle->full_config();
     if (obj->config.has("support_threshold_angle"))
         om.overhang_angle = obj->config.opt_int("support_threshold_angle");
     else {
-        const Slic3r::DynamicPrintConfig& config = wxGetApp().preset_bundle->full_config();
         om.overhang_angle = config.opt_int("support_threshold_angle");
     }
 
+    if (config.has("fan_direction") && config.has("auxiliary_fan")) {
+        FanDirection config_dir = config.option<ConfigOptionEnum<FanDirection>>("fan_direction")->value;
+        if (config_dir == FanDirection::fdUndefine || !config.opt_bool("auxiliary_fan")) {
+            // no part cooling airflow to face, keep the orientation around the z axis unchanged
+            om.cooling_direction = {0, 0, 0};
+        } else if (config_dir == FanDirection::fdRight) {
+            // the part cooling airflow comes from the right side
+            om.cooling_direction = {1, 0, 0};
+            om.has_cooling_fan = true;
+        } else {
+            // the part cooling airflow comes from the left side, or from both sides
+            om.cooling_direction = {-1, 0, 0};
+            om.has_cooling_fan = true;
+        }
+    }
+
     om.setter = [instance](const OrientMesh& p) {
         instance->rotate(p.rotation_matrix);
+        instance->rotate(p.rotation_matrix_vertical);
         instance->get_object()->invalidate_bounding_box();
         instance->get_object()->ensure_on_bed();
     };

src/slic3r/GUI/Tab.cpp

@@ -4956,6 +4956,7 @@ void TabPrinter::build_fff()
         optgroup->append_single_option_line("nozzle_type", "printer_basic_information_accessory#nozzle-type");
         optgroup->append_single_option_line("nozzle_hrc", "printer_basic_information_accessory#nozzle-hrc");
         optgroup->append_single_option_line("auxiliary_fan", "printer_basic_information_accessory#auxiliary-part-cooling-fan");
+        optgroup->append_single_option_line("fan_direction");
         optgroup->append_single_option_line("support_chamber_temp_control", "printer_basic_information_accessory#support-controlling-chamber-temperature");
         optgroup->append_single_option_line("support_air_filtration", "printer_basic_information_accessory#support-air-filtration");
 
@@ -5892,6 +5893,8 @@ void TabPrinter::toggle_options()
 
         const bool support_parallel_printheads = printer_cfg.opt_bool("support_parallel_printheads");
         toggle_line("parallel_printheads_count", support_parallel_printheads);
+
+        toggle_line("fan_direction", m_config->opt_bool("auxiliary_fan"));
     }