Atomic addCombatant with optional CombatantInit bag

addCombatant now accepts an optional init parameter for pre-filled stats
(HP, AC, initiative, creatureId, color, icon, playerCharacterId), making
combatant creation a single atomic operation with domain validation.

This eliminates the multi-step store.save() bypass in addFromBestiary and
addFromPlayerCharacter, and removes the CombatantOpts/applyCombatantOpts
helpers. Also extracts shared initiative sort logic into initiative-sort.ts
used by both addCombatant and setInitiative.

Closes #15

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/domain/src/events.ts

@@ -1,4 +1,5 @@
 import type { ConditionId } from "./conditions.js";
+import type { CreatureId } from "./creature-types.js";
 import type { PlayerCharacterId } from "./player-character-types.js";
 import type { CombatantId } from "./types.js";
 
@@ -19,6 +20,15 @@ export interface CombatantAdded {
 	readonly combatantId: CombatantId;
 	readonly name: string;
 	readonly position: number;
+	readonly init?: {
+		readonly maxHp?: number;
+		readonly ac?: number;
+		readonly initiative?: number;
+		readonly creatureId?: CreatureId;
+		readonly color?: string;
+		readonly icon?: string;
+		readonly playerCharacterId?: PlayerCharacterId;
+	};
 }
 
 export interface CombatantRemoved {