refactor(backend): 添加 service 缓存端口

backend/internal/service/ports/gateway_cache.go

@@ -0,0 +1,13 @@
+package ports
+
+import (
+	"context"
+	"time"
+)
+
+// GatewayCache defines cache operations for gateway service
+type GatewayCache interface {
+	GetSessionAccountID(ctx context.Context, sessionHash string) (int64, error)
+	SetSessionAccountID(ctx context.Context, sessionHash string, accountID int64, ttl time.Duration) error
+	RefreshSessionTTL(ctx context.Context, sessionHash string, ttl time.Duration) error
+}