docs(rewards): drop the stale XP reference from the no-partial-writes comment

The comment sat two lines above the deleted experience computation and
still named XP as something the guard protects. Only silver survives.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/rewards/combat-reward.service.ts

@@ -84,7 +84,7 @@ export class CombatRewardService {
 
     // Resolve every rolled item definition up front, before any mutation, so
     // a missing definition throws `rewardStateInvalid()` before the
-    // character's XP/silver are touched or a `CombatReward` row is created.
+    // character's silver is touched or a `CombatReward` row is created.
     // This keeps a failed grant from leaving partial writes behind.
     const definitions = manager.getRepository(ItemDefinition);
     const resolvedDefinitions = new Map<string, ItemDefinition>();