M4-04: Recover doors and windows with host relationships

[DrunkOnJava]

Created from the roadmap audit in TODO.md.

Source: https://github.com/DrunkOnJava/rvt-rs/blob/main/TODO.md#L584
Tracking commit: 1ec8105

Scope

Labels: priority:P0, type:feature, area:geometry, area:ifc

• Decode family instance placement, host wall id, width, height, sill
  height, hand/facing flips.
• Emit:
  • IfcDoor
  • IfcWindow
  • IfcOpeningElement
  • IfcRelVoidsElement
  • IfcRelFillsElement

Acceptance criteria:

• Known corpus host walls contain openings for doors/windows.
• Door/window counts match manifest.
• Viewer selection shows host relationship.

Definition of done

• The TODO acceptance criteria for this section are implemented or explicitly superseded by a linked decision.
• Tests, fixtures, or documentation are added at the level appropriate to the change risk.
• User-facing behavior and limitations remain honest in README/docs/viewer messaging.
• Relevant CI checks pass before the issue is closed.