Fix in-place alignment editing and curve visualization

- Add clear_layout_segments API to remove segments while preserving alignment ID
- Modify exit_pi_edit_mode to edit segments in-place instead of delete+recreate
- Fix curve visualization by using create_shape for segment vertices
- Fix evaluate_segment validation to handle negative-length curve segments

This prevents "Active alignment no longer exists" errors when editing PIs
and properly renders circular arcs regardless of turn direction.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/ifcopenshell-python/ifcopenshell/api/alignment/util.py

@@ -60,8 +60,18 @@ def evaluate_segment(segment: entity_instance, dist_along: float) -> np.ndarray:
     segment_type = segment.is_a().upper()
     if not segment_type in supported_segment_types:
         raise NotImplementedError(f"Expected entity type 'IFCCURVESEGMENT', got '{segment_type}")
-    if dist_along > segment.SegmentLength:
-        raise ValueError(f"Provided value {dist_along=} is beyond the end of the segment ({segment.SegmentLength}).")
+
+    # Validate dist_along is within segment bounds
+    # SegmentLength can be negative (indicates curve direction), so we need to handle both cases
+    seg_len = segment.SegmentLength.wrappedValue if hasattr(segment.SegmentLength, 'wrappedValue') else segment.SegmentLength
+    if seg_len >= 0:
+        # Positive length: valid range is 0 to seg_len
+        if dist_along < 0 or dist_along > seg_len:
+            raise ValueError(f"Provided value {dist_along=} is beyond the end of the segment ({segment.SegmentLength}).")
+    else:
+        # Negative length: valid range is seg_len to 0
+        if dist_along > 0 or dist_along < seg_len:
+            raise ValueError(f"Provided value {dist_along=} is beyond the end of the segment ({segment.SegmentLength}).")
 
     s = ifcopenshell.geom.settings()
     function_item = ifcopenshell_wrapper.map_shape(s, segment.wrapped_data)