Align zone textures with each theme's palette identity:
- Fabric: linen weave in navy/steel tones (was generic green/blue/red/gray)
- Leather: grain texture in warm brown/amber tones
- VelvetMarble: smooth charcoal marble veining (replaces .jpg with .png)
All zones now have dark + light scheme variants for OS color scheme
adaptation. Plasma zones deferred to separate iteration.
