fix(task-14): polyline bulges leave the backends in WCS, so a mirrored arc reads on its true side

The per-vertex `bulges` list was handed out in the entity's own frame next
to `points` that had been translated to WCS. A mirrored LWPOLYLINE
(extrusion / Normal -Z, what `entity_mirror` produces) is a reflection,
which reverses every arc's sense, so the reader tested endpoints against
the arc's mirror image: a line ending on the true apex dangled, a line
ending on empty paper made a junction, and `length` (frame-invariant)
said nothing. Both engines had it — ezdxf emitted `get_points("xyb")`
raw, COM returned `GetBulge` raw after reflecting `Coordinates`.

`ocs.wcs_bulge(extrusion, bulge)` now negates the sign for a left-handed
frame (the same rule `wcs_arc_angles` applies to an ARC's endpoints) and
both `_entity_info` paths route bulges through it whenever they translate
the points. Fenced by an end-to-end mirrored-pipe graph test, the COM
`_entity_info` fake with Normal -Z, and a boundary-level OCS test.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

backends/ezdxf_backend.py

@@ -815,8 +815,13 @@ def _entity_info_dxf(ent) -> EntityInfo:
             props["length"] = round(_length, 6)
             # The bulge of the segment leaving each vertex (DXF convention), so
             # a reader that walks `points` can test against the arc the drawing
-            # holds instead of the chord it does not. Parallel to `points`.
-            props["bulges"] = [b for _x, _y, b in _verts]
+            # holds instead of the chord it does not. Parallel to `points`, and
+            # in the same frame as them: a mirrored polyline's frame is a
+            # reflection, which reverses every arc's sense, so the stored sign
+            # next to translated points would describe the arc's mirror image.
+            props["bulges"] = [
+                ocs.wcs_bulge(extrusion, b) if needs_ocs else b for _x, _y, b in _verts
+            ]
             if ent.closed:
                 props["area"] = round(_area, 6)
         elif ent_type == "TEXT":