fix(trading-service): use payload.sub as accountSequence in JWT guard

auth-service puts accountSequence in payload.sub, not payload.accountSequence.
This mismatch caused 401 errors when accessing trading endpoints.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/trading-service/src/shared/guards/jwt-auth.guard.ts

@@ -24,7 +24,7 @@ export class JwtAuthGuard implements CanActivate {
     try {
       const secret = this.configService.get<string>('JWT_SECRET', 'default-secret');
       const payload = jwt.verify(token, secret) as any;
-      request.user = { userId: payload.sub, accountSequence: payload.accountSequence };
+      request.user = { accountSequence: payload.sub };
       return true;
     } catch {
       throw new UnauthorizedException('Invalid token');