Splits SimulateCombat into a thin wrapper over simulateCombatWithRNG, a
deterministic core that accepts an optional *rand.Rand. Production passes
nil (package-global rand, behaviorally identical); the new test seeds it
per scenario.
Adds TestCombatCharacterization: 23 curated scenarios x 5 seeds, with the
full event stream + result summary serialized to a stable text form and
diffed against a golden file. This locks current auto-resolve behavior
before the shared-primitives extraction for the turn-based engine — any
perturbation fails loudly and forces a deliberate -update + diff review.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
