Replace Kenney furniture with hospital FBX models (#15)

Swaps all 7 Kenney residential furniture models with proper hospital
3D assets from the Hospital interior asset pack. The new models use
FBX format with a shared colour palette atlas texture.

New models (public/models/hospital/):
  bed.fbx              ← H_Bed_1.fbx (hospital bed with rails)
  chair.fbx            ← H_Chair_1.fbx (ward visitor chair)
  waiting_chair.fbx    ← H_Chair_Clients.fbx (reception waiting chairs)
  computer.fbx         ← H_PC_Monitor.fbx (workstation monitor)
  diagnostic_table.fbx ← H_Stretcher.fbx (examination stretcher)
  medical_equipment.fbx← H_Vital_Signs_Monitor.fbx (vital signs monitor)
  wheelchair.fbx       ← H_Wheelchair.fbx (actual wheelchair)
  curtain.fbx          ← H_Curtain_1.fbx (privacy curtain, decoration)
  iv_stand.fbx         ← H_Serum.fbx (IV stand, decoration)
  reception_desk.fbx   ← H_Reception_Desk.fbx (decoration)
  plant.fbx            ← H_Plant.fbx (decoration)
  + 3 texture atlas PNGs (colour, metallic, roughness)

ThreeFloorPlan changes:
- Switched from useGLTF (Kenney GLB) to FBXLoader for furniture.
- FBXLoader.setResourcePath points at /models/hospital/ so the
  loader can find the shared texture atlas automatically.
- Materials kept as Phong (what the FBX models were designed for)
  with the colour atlas applied as the texture map.
- Module-level fbxCache and textureCache ensure each model URL and
  the atlas are loaded exactly once across all placements.
- Lighting boosted: ambient 1.5, hemisphere 0.6, directional 1.8,
  tone mapping set to NoToneMapping for accurate flat-shaded colours.

The Kenney GLB models in public/models/ are retained as fallbacks.

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

Author: stedrew