Use Hospital pack FBX models for walls and floors (#15)

Replaces the plain BoxGeometry walls and PlaneGeometry floors with
actual FBX models from the Hospital interior asset pack. The walls
now have cream/green body, blue accent stripe, and brown baseboard
matching the pack's preview images.

Walls:
- wall_small_ward.fbx (1000mm = 1 tile) tiled at 1-tile intervals
  along each parser wall segment. Horizontal walls placed at rotY=0,
  vertical walls at rotY=PI/2.

Floors:
- floor_ward.fbx (beige, 1000mm) for treatment rooms
- floor_reception.fbx (blue tile, 2000mm) for waiting/reception areas
- floor_office.fbx (neutral, 1000mm) for hallway/exit
- Tiled per-tile across each zone's tile positions (not bounding box)
  so only actual zone tiles get a floor model.

Also added wall_medium_ward, wall_window_ward, wall_door_ward,
wall_corner_ward, floor_ward_big, and decoration models (curtain,
iv_stand, cabinet, reception_desk, plant, doors) to public/models/
for future use.

Scale: 0.001 (FBX mm → Three.js units where 1 unit = 1 tile).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stedrew