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/PrintConfig.hpp

@@ -362,6 +362,13 @@ enum LayerSeq {
     flsCustomize
 };
 
+enum FanDirection {
+    fdUndefine = 0,
+    fdLeft,
+    fdRight,
+    fdBoth
+};
+
 static std::unordered_map<NozzleType, std::string>NozzleTypeEumnToStr = {
     {NozzleType::ntUndefine,        "undefine"},
     {NozzleType::ntHardenedSteel,   "hardened_steel"},
@@ -1494,6 +1501,7 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionEnumsGenericNullable,nozzle_type))
     ((ConfigOptionInt,                 nozzle_hrc))
     ((ConfigOptionBool,                auxiliary_fan))
+    ((ConfigOptionEnum<FanDirection>,  fan_direction))
     ((ConfigOptionBool,                support_air_filtration))
     ((ConfigOptionBool,                cooling_filter_enabled))
     ((ConfigOptionEnum<PrinterStructure>,printer_structure))