refactor(backend): 添加 service 缓存端口

backend/internal/service/ports/identity_cache.go

@@ -0,0 +1,21 @@
+package ports
+
+import "context"
+
+// Fingerprint represents account fingerprint data
+type Fingerprint struct {
+	ClientID                string
+	UserAgent               string
+	StainlessLang           string
+	StainlessPackageVersion string
+	StainlessOS             string
+	StainlessArch           string
+	StainlessRuntime        string
+	StainlessRuntimeVersion string
+}
+
+// IdentityCache defines cache operations for identity service
+type IdentityCache interface {
+	GetFingerprint(ctx context.Context, accountID int64) (*Fingerprint, error)
+	SetFingerprint(ctx context.Context, accountID int64, fp *Fingerprint) error
+}