refactor(inventory): flatten effects directory structure

Move effect handlers from effects/ subdirectory to flat structure:
- effects/handlers.ts → effect.handlers.ts
- effects/registry.ts → effect.registry.ts
- effects/types.ts → effect.types.ts

Update import path in inventory.service.ts from
'@/modules/inventory/effects/registry' to
'@/modules/inventory/effect.registry'.

This reduces directory nesting and follows the convention of
keeping module files flat unless there are 5+ files.

bot/modules/inventory/effect.handlers.ts

@@ -1,7 +1,7 @@
 import { levelingService } from "@shared/modules/leveling/leveling.service";
 import { economyService } from "@shared/modules/economy/economy.service";
 import { userTimers } from "@db/schema";
-import type { EffectHandler } from "./types";
+import type { EffectHandler } from "./effect.types";
 import type { LootTableItem } from "@shared/lib/types";
 import { inventoryService } from "@shared/modules/inventory/inventory.service";
 import { inventory, items } from "@db/schema";

bot/modules/inventory/effect.registry.ts

@@ -6,8 +6,8 @@ import {
     handleTempRole,
     handleColorRole,
     handleLootbox
-} from "./handlers";
+} from "./effect.handlers";
-import type { EffectHandler } from "./types";
+import type { EffectHandler } from "./effect.types";
 
 export const effectHandlers: Record<string, EffectHandler> = {
     'ADD_XP': handleAddXp,

bot/modules/inventory/effect.types.ts

@@ -1,4 +1,3 @@
-
 import type { Transaction } from "@shared/lib/types";
 
 export type EffectHandler = (userId: string, effect: any, txFn: Transaction) => Promise<any>;

shared/modules/inventory/inventory.service.ts

@@ -171,7 +171,7 @@ export const inventoryService = {
             const results: any[] = [];
 
             // 2. Apply Effects
-            const { effectHandlers } = await import("@/modules/inventory/effects/registry");
+            const { effectHandlers } = await import("@/modules/inventory/effect.registry");
 
             for (const effect of usageData.effects) {
                 const handler = effectHandlers[effect.type];