feat: internationalize API error responses by locale

Add shared error codes with zh/en/ms messages, coded app exceptions,
and locale-aware global filter. Frontends send X-Locale so error text
matches the active UI language.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/domains/betting/betting-limits.service.ts

@@ -1,6 +1,7 @@
-import { Injectable, BadRequestException } from '@nestjs/common';
+import { Injectable } from '@nestjs/common';
 import { Decimal } from '@prisma/client/runtime/library';
 import { PrismaService } from '../../shared/prisma/prisma.service';
+import { appBadRequest } from '../../shared/common/app-error';
 
 export type BettingLimits = {
   minStake: number;
@@ -89,18 +90,18 @@ export class BettingLimitsService {
     const stake = params.stake;
 
     if (stake < limits.minStake) {
-      throw new BadRequestException(`Minimum stake is ${limits.minStake}`);
+      throw appBadRequest('MIN_STAKE', { minStake: limits.minStake });
     }
 
     const maxStake = params.betType === 'PARLAY' ? limits.maxStakeParlay : limits.maxStakeSingle;
     if (stake > maxStake) {
-      throw new BadRequestException(`Maximum stake is ${maxStake}`);
+      throw appBadRequest('MAX_STAKE', { maxStake });
     }
 
     const maxPayout =
       params.betType === 'PARLAY' ? limits.maxPayoutParlay : limits.maxPayoutSingle;
     if (params.potentialReturn.gt(maxPayout)) {
-      throw new BadRequestException(`Potential return exceeds limit of ${maxPayout}`);
+      throw appBadRequest('MAX_PAYOUT', { maxPayout });
     }
 
     if (limits.dailyStakeLimit > 0) {
@@ -119,7 +120,7 @@ export class BettingLimitsService {
       });
       const todayStake = new Decimal(agg._sum.stake ?? 0);
       if (todayStake.add(stake).gt(limits.dailyStakeLimit)) {
-        throw new BadRequestException(`Daily stake limit of ${limits.dailyStakeLimit} exceeded`);
+        throw appBadRequest('DAILY_STAKE_LIMIT', { limit: limits.dailyStakeLimit });
       }
     }
   }