Implement the 016-combatant-ac feature that adds an optional Armor Class field to combatants with shield icon display and inline editing in the encounter tracker

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/domain/src/events.ts

@@ -68,6 +68,13 @@ export interface RoundRetreated {
 	readonly newRoundNumber: number;
 }
 
+export interface AcSet {
+	readonly type: "AcSet";
+	readonly combatantId: CombatantId;
+	readonly previousAc: number | undefined;
+	readonly newAc: number | undefined;
+}
+
 export type DomainEvent =
 	| TurnAdvanced
 	| RoundAdvanced
@@ -78,4 +85,5 @@ export type DomainEvent =
 	| MaxHpSet
 	| CurrentHpAdjusted
 	| TurnRetreated
-	| RoundRetreated;
+	| RoundRetreated
+	| AcSet;