Update slaughterhouse

#### Icon Update
- The current `slaughterhouse` icon should be centered
- It also is not aligned to the pixel grid
- Is there a better way to represent this?

Locate the existing `slaughterhouse` icon in the Maki icon set and inspect its current alignment and pixel-grid placement. Update the icon so it is centered and aligned to the pixel grid, then assess whether the current representation should be improved; the issue provides no named file or test, so completion is visual review against those criteria.

Written by the indexing model from the issue text.