[0.6.x + 0.7.0 pre2] Nomad Physics

**0.1.1**

Added three placeable demo blocks to the physics core:

- **Rubber Block:** matte red rubber with rounded corners and bounces that lose height until it settles. Tuned for strong rebounds while staying grippy.
- **Steel Weight:** four times the ordinary block mass for heavier impacts against loose props.
- **Slick Block:** slides farther while loose and gives players an ice-like surface to slide on when placed.

Find them under **Blocks > Build** in the creative catalog, or use `/give <player> Nomad_Demo_Rubber`, `Nomad_Demo_Steel`, or `Nomad_Demo_Slick`. Both physics guns can pick them up in block mode. Each block keeps its material behavior after settling and being picked up again.

Updated the demo models, textures and inventory icons. Clarified the tool guide: F toggles block mode when nothing is held; normal grab inputs pick up blocks, and the physgun handles freezing and rotation. Plugin authors can now set friction and restitution through `AdoptOptions`; the existing five-argument constructor remains compatible.