v0.32.1 — self-documenting gate-file decision shape

Fixed

• Self-documenting gate-file decisions (#72). The emitted *.gate.json showed
  "decision": null with no shape hint, and the obvious fill ("decision": "reuse")
  was silently coerced to None and mislabeled "no decision filled in" — stalling
  the documented happy path. Now the gate-file scaffolds "decision": {"choice": null}
  plus a _hint; a bare string is accepted and normalized to {"choice": "reuse"};
  and read_gate_decision distinguishes a genuinely-empty decision from a wrong-shape
  one (decision must be an object like {"choice": ...}; got [...]). The engine was
  already correct — only the affordance is fixed.