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/index.ts

@@ -1,4 +1,8 @@
-export { type AddCombatantSuccess, addCombatant } from "./add-combatant.js";
+export {
+	type AddCombatantSuccess,
+	addCombatant,
+	type CombatantInit,
+} from "./add-combatant.js";
 export { type AdjustHpSuccess, adjustHp } from "./adjust-hp.js";
 export { advanceTurn } from "./advance-turn.js";
 export { resolveCreatureName } from "./auto-number.js";