Issue #2 gap: Added 14 CardDefinition validation tests covering all
required field checks (hp, stage, pokemon_type, evolves_from, trainer_type,
energy_type) with both negative and positive test cases.
Issue #7 gap: Added 4 confusion attack engine tests covering heads/tails
outcomes, self-damage, self-KO with opponent scoring, and configurable
damage from RulesConfig.
Issue #13 documentation: Added TODO comments in engine.py and handlers.py
documenting the expected pattern for knockout detection when effect
execution is implemented. Effect handlers set knockout flags; engine
should process knockouts after all effects resolve.
825 tests passing (+17 new tests)
5f1eb11344