fix: API rate limit 60→120 req/min 상향

지갑 페이지에서 GET 호출이 다수 발생하여 429 빈번히 발생하던 문제 완화.

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

internal/server/server.go

@@ -59,10 +59,10 @@ func AuthLimiter() fiber.Handler {
 	})
 }
 
-// APILimiter returns a rate limiter for general API endpoints (60 req/min per IP).
+// APILimiter returns a rate limiter for general API endpoints (120 req/min per IP).
 func APILimiter() fiber.Handler {
 	return limiter.New(limiter.Config{
-		Max:        60,
+		Max:        120,
 		Expiration: 1 * time.Minute,
 		KeyGenerator: func(c *fiber.Ctx) string {
 			return c.IP()