Add scripted event withdrawals

docs/ARCHITECTURE.md

@@ -43,7 +43,7 @@
 8. Player ends turn.
 9. Enemy AI moves, picks physical attacks from damage, defeat, priority, and weapon-effectiveness scores, and can cast single-target or area damage, healing, support, debuff, movement-modifier, accuracy/evasion-modifier, damage-over-time, or action-lock tactics through the same combat and skill resolvers.
 10. Battle checks scenario-defined defeat conditions first, including commander loss and turn limits, then victory conditions such as enemy defeat or reaching a marked destination tile.
-11. Turn-start and movement-triggered scenario events run as phases change or units enter marked cells, and may update objectives with HUD notices, grant inventory pickups, or deploy reinforcements.
+11. Turn-start and movement-triggered scenario events run as phases change or units enter marked cells, and may update objectives with HUD notices, grant inventory pickups, deploy reinforcements, or withdraw units from the battlefield.
 12. On first-time victory, `CampaignState` snapshots player progression and the battle inventory, applies rewards once, advances `current_scenario_id`, and writes `user://campaign_save.json`.
 13. If the scenario defines post-battle dialogue, it plays once before the victory result panel opens.
 14. The victory result panel splits rewards, roster changes, saved player growth, campaign status, and pending choices into sections.