feat: enforce active quest limit in assignQuest

Adds a limit check to assignQuest that reads maxActiveQuests from game
settings and throws a UserError when the user has reached their active
quest limit. Completed quests are excluded from the count.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

shared/modules/quest/quest.service.ts

@@ -4,6 +4,7 @@ import { UserError } from "@shared/lib/errors";
 import { DrizzleClient } from "@shared/db/DrizzleClient";
 import { economyService } from "@shared/modules/economy/economy.service";
 import { levelingService } from "@shared/modules/leveling/leveling.service";
+import { gameSettingsService } from "@shared/modules/game-settings/game-settings.service";
 import { withTransaction } from "@/lib/db";
 import type { Transaction } from "@shared/lib/types";
 import { TransactionType } from "@shared/lib/constants";
@@ -12,13 +13,29 @@ import { systemEvents, EVENTS } from "@shared/lib/events";
 export const questService = {
     assignQuest: async (userId: string, questId: number, tx?: Transaction) => {
         return await withTransaction(async (txFn) => {
+            // Check active quest limit
+            const settings = await gameSettingsService.getSettings();
+            const maxActive = settings?.quest?.maxActiveQuests ?? 3;
+
+            const userQuestList = await txFn.query.userQuests.findMany({
+                where: eq(userQuests.userId, BigInt(userId)),
+            });
+
+            const activeCount = userQuestList.filter(uq => !uq.completedAt).length;
+
+            if (activeCount >= maxActive) {
+                throw new UserError(
+                    `You can only have ${maxActive} active quests at a time. Complete a quest before accepting a new one.`
+                );
+            }
+
             return await txFn.insert(userQuests)
                 .values({
                     userId: BigInt(userId),
                     questId: questId,
                     progress: 0,
                 })
-                .onConflictDoNothing() // Ignore if already assigned
+                .onConflictDoNothing()
                 .returning();
         }, tx);
     },