- Add x_offset/z_offset to PositionedBlock for multi-block furniture clusters
- Furniture items now spread across 2-3 positions (matching original Java code)
- Offsets multiplied by inward direction for correct corner orientation
- Fix has_ceiling_chain: only oubliette has ceiling chains (was true for all 6)
- Fix firstCornerSpecial: oubliette cauldron uses x/z offset +1 (inward diagonal)
- Update parser to read x_offset/z_offset (defaults to 0)