refactor(backend): 添加 service 缓存端口

backend/internal/service/ports/redeem_cache.go

@@ -0,0 +1,15 @@
+package ports
+
+import (
+	"context"
+	"time"
+)
+
+// RedeemCache defines cache operations for redeem service
+type RedeemCache interface {
+	GetRedeemAttemptCount(ctx context.Context, userID int64) (int, error)
+	IncrementRedeemAttemptCount(ctx context.Context, userID int64) error
+
+	AcquireRedeemLock(ctx context.Context, code string, ttl time.Duration) (bool, error)
+	ReleaseRedeemLock(ctx context.Context, code string) error
+}