feat(entities): surface remaining 2D + Region fields in properties

Closes out the 2D-entity audit (and the Region partner that ships next
to Solid3D / Body). Round-trip-only metadata fields plus a few editable
ones gain Properties-panel rows so the values the parser populates are
visible and don't get silently dropped on save:

- Hatch: seed_points count, pixel_size, normal
- Polyline2D: smooth_surface, default_start_width, default_end_width,
  thickness, normal (with editors for the widths/thickness)
- Region: uid, silhouettes (shared file with Solid3D / Body)
- Underlay: clip_inverted
- RasterImage: class_version, definition_handle, definition_reactor_handle
- Wipeout: class_version, clip_mode, definition_handle,
  definition_reactor_handle
- Leader: annotation_handle, override_color
- Tolerance: dimension_style_name, dimension_style_handle, dimension_gap,
  text_height (editable), direction, normal
- MLine: style_handle, style_element_count, justification picker
- Ole2Frame: version, source_application, binary_data size, dwg_mode,
  dwg_trailing_byte, is_paper_space
- Viewport: snap_base/spacing/angle, twist_angle, front/back clip Z,
  circle_sides, grid_flags, grid_major, base_ucs_handle, ucs_ortho_type,
  background_handle, shade_plot_handle, visual_style_handle,
  default_lighting, default_lighting_type, ambient_color (with editors
  for the snap / clip / circle_sides values)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/entities/hatch.rs

@@ -63,6 +63,17 @@ fn properties(h: &Hatch) -> PropSection {
                 if h.is_associative { "Yes" } else { "No" },
             ),
             edit("Elevation", "elevation", h.elevation),
+            ro("Seed Points", "seed_count", h.seed_points.len().to_string()),
+            ro(
+                "Pixel Size",
+                "pixel_size",
+                format!("{:.6}", h.pixel_size),
+            ),
+            ro(
+                "Normal",
+                "normal",
+                format!("{:.3}, {:.3}, {:.3}", h.normal.x, h.normal.y, h.normal.z),
+            ),
         ],
     }
 }