refactor(backend): 添加 service 缓存端口

backend/internal/service/ports/email_cache.go

@@ -0,0 +1,20 @@
+package ports
+
+import (
+	"context"
+	"time"
+)
+
+// VerificationCodeData represents verification code data
+type VerificationCodeData struct {
+	Code      string
+	Attempts  int
+	CreatedAt time.Time
+}
+
+// EmailCache defines cache operations for email service
+type EmailCache interface {
+	GetVerificationCode(ctx context.Context, email string) (*VerificationCodeData, error)
+	SetVerificationCode(ctx context.Context, email string, data *VerificationCodeData, ttl time.Duration) error
+	DeleteVerificationCode(ctx context.Context, email string) error
+}