CLASS-11: Window decoder (carve out from M4-04 doors/windows; v0.2.0 has door pipeline only)

[DrunkOnJava]

Problem

v0.2.0's M4-04 umbrella covers doors AND windows, but the
shipped RE-14 pipeline only emits doors. Windows are still
unhandled. 2024_Core_Interior.rvt has windows in Revit's IFC
export that rvt-ifc does not yet emit.

Scope

• Identify the ElemTable tuple(s) marking windows (likely a
  FamilyInstance subtype distinguished by category or family
  symbol reference).
• Add ProbableClass::Window mapping(s).
• Emit IFCWINDOW entities with same opening/void/fill triples
  as RE-15-09 for doors.
• Decode width/height/sill from FamilyInstance dimensions.

Acceptance criteria

• At least 30 IFCWINDOW entities emitted on
  2024_Core_Interior.rvt (window count to be verified
  against Revit IFC export).
• Host wall voids correctly cut for windows.
• Corpus regression test pinned to threshold.

Related

• Umbrella: M4-04: Recover doors and windows with host relationships #32 (M4-04) — covers both doors + windows
• Pairs with RE-15-09 (door geometry/voids)