[M0-S8] Generate neighbour and transition chunks #63

Problem

A stage is a grid explored in four directions; new chunks must continue their neighbours exactly.

Acceptance criteria

• make_boards.py neighbour --dir up|down|left|right produces a chunk from an edge band
• A transition chunk (surface → underground) is generated with both neighbours as context

Notes and dependencies

See 04 – Explored in four directions. Not needed for the jam slice.

Verification

The shared band is pixel-identical; the review page shows both chunks side by side.