chore: 回退至稳定版本，清理测试文件

- 回退 VLM prompt 至稳定的通用食物识别版本
- 保持 VisionClient 重命名和 VLM_* 配置键
- 清理所有测试图片和临时文件

backend/src/Health.WebApi/Endpoints/ai_chat_endpoints.cs

@@ -232,7 +232,7 @@ public static class AiChatEndpoints
         // VLM 食物识别
         app.MapPost("/api/ai/analyze-food-image", async (
             HttpRequest httpRequest, HttpContext http,
-            QwenVisionClient visionClient, AppDbContext db,
+            VisionClient visionClient, AppDbContext db,
             CancellationToken ct) =>
         {
             var userId = GetUserId(http);
@@ -242,8 +242,6 @@ public static class AiChatEndpoints
             var files = form.Files.GetFiles("images");
             if (files == null || files.Count == 0)
                 return Results.Ok(new { code = 40001, data = (object?)null, message = "请上传至少一张图片" });
-            if (files.Count > 8)
-                return Results.Ok(new { code = 40001, data = (object?)null, message = "一次最多上传 8 张图片" });
 
             var imageUrls = new List<string>();
             var uploadsDir = Path.Combine(Directory.GetCurrentDirectory(), "uploads");
@@ -272,19 +270,9 @@ public static class AiChatEndpoints
             }
 
             var prompt = """
-                你是一个专业营养师。请仔细分析这些食物照片（可能是同一餐不同角度拍摄）。
-
-                要求：
-                1. 识别所有食物，用中文名称
-                2. 根据多角度照片综合判断份量，尽量精准
-                3. 估算每项的热量、蛋白质、碳水、脂肪（克）
-
-                只返回JSON：
+                识别图片中所有食物，用中文名称，只返回JSON：
                 {
-                  "foods": [
-                    {"name":"食物名","portion":"份量描述","calories":整数,"proteinGrams":整数,"carbsGrams":整数,"fatGrams":整数}
-                  ],
-                  "totalCalories":整数
+                  "foods": [{"name":"食物名","portion":"份量","calories":整数}]
                 }
                 """;
 

backend/src/Health.WebApi/Program.cs

@@ -73,10 +73,10 @@ builder.Services.AddHttpClient<DeepSeekClient>(client =>
     client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", builder.Configuration["DEEPSEEK_API_KEY"] ?? "");
     client.Timeout = TimeSpan.FromSeconds(60);
 });
-builder.Services.AddHttpClient<QwenVisionClient>(client =>
+builder.Services.AddHttpClient<VisionClient>(client =>
 {
-    client.BaseAddress = new Uri((builder.Configuration["QWEN_BASE_URL"] ?? "https://dashscope.aliyuncs.com/compatible-mode/v1").TrimEnd('/') + "/");
-    client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", builder.Configuration["QWEN_API_KEY"] ?? "");
+    client.BaseAddress = new Uri((builder.Configuration["VLM_BASE_URL"] ?? "https://dashscope.aliyuncs.com/compatible-mode/v1").TrimEnd('/') + "/");
+    client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", builder.Configuration["VLM_API_KEY"] ?? "");
     client.Timeout = TimeSpan.FromSeconds(60);
 });