Previously _resolve_combat() used a binary power-vs-toughness kill check:
creatures only died if a single source had power >= their toughness in one
swing. This meant a 2/2 wouldn't die to two 1/1 tokens blocking it, and
repeated smaller hits across combats never accumulated.
Changes:
- models.py: add damage_marked field to Card (default 0)
- engine.py: accumulate damage via damage_marked += power instead of
binary a_pow >= toughness checks in _resolve_combat()
- engine.py: clear damage_marked = 0 in untap phase (MTG rule 514.2)
This enables multi-blocker lethality, incremental chip damage within a
combat step, and proper creature death-by-accumulated-damage interactions.
KoalaTrapLord
cffd8d8109