feat: Introduce TimerKey enum and refactor timer key usage across services with new tests.

shared/modules/leveling/leveling.service.ts

@@ -3,7 +3,7 @@ import { eq, sql, and } from "drizzle-orm";
 import { withTransaction } from "@/lib/db";
 import { config } from "@shared/lib/config";
 import type { Transaction } from "@shared/lib/types";
-import { TimerType } from "@shared/lib/constants";
+import { TimerKey, TimerType } from "@shared/lib/constants";
 
 export const levelingService = {
     // Calculate total XP required to REACH a specific level (Cumulative)
@@ -84,7 +84,7 @@ export const levelingService = {
                 where: and(
                     eq(userTimers.userId, BigInt(id)),
                     eq(userTimers.type, TimerType.COOLDOWN),
-                    eq(userTimers.key, 'chat_xp')
+                    eq(userTimers.key, TimerKey.CHAT_XP)
                 ),
             });
 
@@ -120,7 +120,7 @@ export const levelingService = {
                 .values({
                     userId: BigInt(id),
                     type: TimerType.COOLDOWN,
-                    key: 'chat_xp',
+                    key: TimerKey.CHAT_XP,
                     expiresAt: nextReadyAt,
                 })
                 .onConflictDoUpdate({