- Introduce `bus_wheel_2` asset and register it in the asset manifest
- Add `BUS.wheelRadius2` config for the larger wheel radius
- Extend themes with a `bus` block to select wheel texture and radius per campaign; campaign02 uses the new bigger wheels while keeping the same axle center
- Make `Bus` accept a bus theme parameter and use provided wheel texture/radius when creating wheels
- Update `PlayScene` to pass the active theme's `bus` settings into the Bus constructor
- Document the new per-campaign bus art/sizing behavior in sprites.md
