pixels package

Package pixels is the real, permanent GNO Pixels realm -- gno.land/r/pixelsandbox (this project's earlier scratch deployment, never redeployable in place once live) was always the deliberately generic placeholder name described in this project's own README, kept around exactly so the design could keep changing without colliding with whatever this real deployment ended up being called.

Expandable bounds instead of a fixed size, per-pixel provenance (who placed it, at what block), and an owner-gated import hook for migrating the scratch realm's already-placed pixels into this one.