Subtracts the DXF header extents centroid (world_offset) from all coordinates
in f64 BEFORE casting to f32. This eliminates the ~0.5 m ULP error that occurs
at 4,000,000 m UTM coordinates and caused geometry to disappear on zoom-out.
- Scene: adds world_offset field + compute_and_set_world_offset() method
- tessellate.rs: threads world_offset through all f64→f32 conversions
(legacy_geometry, dimension_geometry, solid_wire_fallback, multileader)
- truck_tess.rs: to_local() helper already in place from prior session
- mod.rs: tessellate_entity() and entity_aabb() apply world_offset
- update.rs: compute_and_set_world_offset() called after doc load
- cmd_result.rs / solid3d_cmds.rs: pass correct offset to truck tessellators
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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