Sinor Building Props - Rust Skins

• Rust skin model pack for `sinor-BaseBuilding`

• Every Rust model uses the matching original building-prop name with `_rust`

added at the end. For example:

-sinor_prop_wall_wood       -> sinor_prop_wall_wood_rust

-sinor_prop_ceiling_square_metal -> sinor_prop_ceiling_square_metal_rust

• The skin system in `sinor-BaseBuilding` detects these names automatically.