Implement the 025-display-initiative feature that adds initiative modifier and passive initiative display to creature stat blocks, calculated as DEX modifier + (proficiency multiplier × proficiency bonus) from bestiary data, shown in MM 2024 format on the AC line

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

packages/domain/src/index.ts

@@ -47,6 +47,11 @@ export type {
 	TurnRetreated,
 } from "./events.js";
 export { deriveHpStatus, type HpStatus } from "./hp-status.js";
+export {
+	calculateInitiative,
+	formatInitiativeModifier,
+	type InitiativeResult,
+} from "./initiative.js";
 export {
 	type RemoveCombatantSuccess,
 	removeCombatant,