Track commander damage at combat-damage time by checking `is_commander`
on each attacking creature. Damage from commander creatures is now
recorded in both a per-seat aggregate (`commander_damage_received`) and
a per-card breakdown (`commander_damage_by_card`), enabling correct
21-damage lethal checks for partner/multi-commander games.
Changes:
- engine._resolve_combat: identify commander attackers, accumulate their
damage (including trample overflow and double strike), write to both
tracking dicts, and check commander-damage elimination after combat.
- models.Player: add commander_damage_received, commander_damage_by_card,
and is_dead_to_commander_damage() so the headless engine can track
commander damage without the full CommanderGameState wrapper.
- game_state.CommanderPlayer: replace the separate
commander_damage_received field with a property delegating to
base.Player to avoid split-brain state between engine and wrapper.
- game_state.CommanderGameState.deal_commander_damage: accept optional
commander_name for per-card tracking.
- 22 new regression tests covering unblocked, blocked, trample, double
strike, lifelink, partner, cumulative, and lethal scenarios.
Partial fix for Issue #86 item 2.
Co-authored-by: Claude <noreply@anthropic.com>
