Token movement + mining + death

[uncomposed]

Acceptance Criteria:

• Move costs 1 MP; token updates atomically per step.
• After moving, mine surface value v and add to MP.
• If MP ≤ 0 after mining, token is removed.
• Edge: MP=1 → step onto +2 → survives with MP=2.
• Edge: MP=1 → step onto 0 → dies end of turn.