Add poison damage over time tactics

docs/GODOT_4_6_MIGRATION.md

@@ -46,6 +46,7 @@ powershell -NoProfile -ExecutionPolicy Bypass -File tools\check_godot46_readines
 - Finite-stock Shop entries show remaining counts and disable once sold out.
 - Manual checkpoint save/load restores the expected current briefing without script errors.
 - A player unit can move, attack, wait, use a tactic, use an item, and equip compatible gear.
+- Poison Mist applies poison, poison ticks at the target team's phase start, and poison defeat immediately ends the battle when it satisfies a victory or defeat condition.
 - Enemy turn advances and AI acts.
 - Victory and defeat panels still appear.
 - Post-battle dialogue and post-battle choices still block progression until a choice is saved.