feat: Implement face clustering management service and API

Services/AI/IFaceClusteringService.cs

@@ -0,0 +1,24 @@
+using Foxel.Models.DataBase;
+
+public interface IFaceClusteringService
+{
+    /// <summary>
+    /// 对所有未分类的人脸进行聚类
+    /// </summary>
+    Task<List<FaceCluster>> ClusterFacesAsync();
+    
+    /// <summary>
+    /// 对指定用户的未分类人脸进行聚类
+    /// </summary>
+    Task<List<FaceCluster>> ClusterUserFacesAsync(int userId);
+    
+    /// <summary>
+    /// 为新检测到的人脸分配到现有聚类或创建新聚类
+    /// </summary>
+    Task<FaceCluster?> AssignFaceToClusterAsync(int faceId);
+    
+    /// <summary>
+    /// 计算两个人脸嵌入向量的相似度
+    /// </summary>
+    double CalculateSimilarity(float[] embedding1, float[] embedding2);
+}