Add Y-flip swap for vertical pin rotation in sexp fallback

Pin angles in lib_symbol use Y-up convention. After applying component
rotation, vertical directions (90/270) must be swapped to account for
the lib Y-up to schematic Y-down coordinate transform. Without this,
vertical stubs on non-mirrored components point into the body instead
of away from it, causing label_multiple_wires ERC violations.

src/mckicad/utils/sexp_parser.py

@@ -1128,11 +1128,22 @@ def resolve_pin_position_and_orientation(
         target_pin["x"], target_pin["y"], cx, cy, comp_rot, mirror_x,
     )
 
-    # Compute schematic-space pin rotation
+    # Compute schematic-space pin rotation.
+    # Pin angles in lib_symbol use Y-up convention.  After applying the
+    # component rotation, vertical directions must be swapped (90 <-> 270)
+    # to account for the lib Y-up -> schematic Y-down coordinate flip.
+    # For mirrored components, the mirror is applied first.
     pin_rot = target_pin["rotation"]
     if mirror_x:
         pin_rot = (180 - pin_rot) % 360
     schematic_rot = (pin_rot + comp_rot) % 360
+    # Y-flip: swap vertical directions for non-mirrored components.
+    # Mirror already handles the inversion via (180 - pin_rot).
+    if not mirror_x:
+        if schematic_rot == 90:
+            schematic_rot = 270
+        elif schematic_rot == 270:
+            schematic_rot = 90
 
     logger.debug(
         "Resolved pin %s.%s via sexp fallback: (%.2f, %.2f) @ %.0f°",