feat: 新增向量嵌入服务支持

新增SiliconFlow向量嵌入服务实现，支持文本向量化功能：
- 新增ITextEmbeddingService接口和SiliconFlowTextEmbeddingService实现
- 新增EmbeddingCreateRequest/Response等向量相关DTO
- 在AiGateWayManager中新增EmbeddingForStatisticsAsync方法
- 在OpenApiService中新增向量生成API接口
- 扩展ModelTypeEnum枚举支持Embedding类型
- 优化ThorChatMessage的Content属性处理逻辑

Yi.Abp.Net8/module/ai-hub/Yi.Framework.AiHub.Domain/AiGateWay/Impl/ThorSiliconFlow/Embeddings/SiliconFlowTextEmbeddingService.cs

@@ -0,0 +1,24 @@
+using System.Net.Http.Json;
+using Yi.Framework.AiHub.Application.Contracts.Dtos.OpenAi.Embeddings;
+using Yi.Framework.AiHub.Domain.Shared.Dtos;
+
+namespace Yi.Framework.AiHub.Domain.AiGateWay.Impl.ThorSiliconFlow.Embeddings;
+
+public sealed class SiliconFlowTextEmbeddingService
+    : ITextEmbeddingService
+{
+    public async Task<EmbeddingCreateResponse> EmbeddingAsync(
+        EmbeddingCreateRequest createEmbeddingModel,
+        AiModelDescribe? options = null,
+        CancellationToken cancellationToken = default)
+    {
+        var response = await HttpClientFactory.GetHttpClient(options.Endpoint).PostJsonAsync(
+            options?.Endpoint.TrimEnd('/') + "/v1/embeddings",
+            createEmbeddingModel, options!.ApiKey);
+
+        var result =
+            await response.Content.ReadFromJsonAsync<EmbeddingCreateResponse>(cancellationToken: cancellationToken);
+
+        return result;
+    }
+}