feat: UI全面改造 + 后端多项修复

【后端修复】
- 删除diet/consultation agent假工具声明
- 修复DayOfWeek实体注释
- 修复Vision API content序列化
- cleanup_service级联删除修复
- 用药提醒时区偏差修复
- 统一DateTime处理(UtcNow+8)
- 新增UTC DateTime JSON转换器

【前端UI重构】
- 配色体系全面更新(#8B5CF6淡紫+#F0ECFF背景)
- 登录页重设计
- 首页重设计(透明顶栏、渐变背景、胶囊输入区)
- 聊天卡片加白蓝边框、渐变标题
- 侧边栏重构(渐变背景、合并顶部、删除底部设置)
- 确认卡片可编辑字段恢复
- 所有子页面加返回按钮
- catch异常加日志
- 删除后refresh provider缓存

backend/src/Health.Infrastructure/Data/dev_data_seeder.cs

@@ -104,7 +104,7 @@ public static class DevDataSeeder
         });
 
         // ---- 运动计划 ----
-        var monday = DateOnly.FromDateTime(DateTime.Now.AddDays(-(int)DateTime.Now.DayOfWeek + 1));
+        var monday = DateOnly.FromDateTime(DateTime.UtcNow.AddHours(8).AddDays(-(int)DateTime.UtcNow.AddHours(8).DayOfWeek + 1));
         var plan = new ExercisePlan { Id = Guid.NewGuid(), UserId = user.Id, WeekStartDate = monday };
         plan.Items.Add(new ExercisePlanItem { Id = Guid.NewGuid(), DayOfWeek = 0, ExerciseType = "散步", DurationMinutes = 30, IsCompleted = true, CompletedAt = DateTime.UtcNow.AddDays(-1) });
         plan.Items.Add(new ExercisePlanItem { Id = Guid.NewGuid(), DayOfWeek = 1, ExerciseType = "慢跑", DurationMinutes = 20 });
@@ -119,7 +119,7 @@ public static class DevDataSeeder
         var lunch = new DietRecord
         {
             Id = Guid.NewGuid(), UserId = user.Id, MealType = MealType.Lunch,
-            TotalCalories = 644, HealthScore = 3, RecordedAt = DateOnly.FromDateTime(DateTime.Now),
+            TotalCalories = 644, HealthScore = 3, RecordedAt = DateOnly.FromDateTime(DateTime.UtcNow.AddHours(8)),
         };
         lunch.FoodItems.Add(new DietFoodItem { Id = Guid.NewGuid(), Name = "米饭", Portion = "约1碗", Calories = 174, SortOrder = 1 });
         lunch.FoodItems.Add(new DietFoodItem { Id = Guid.NewGuid(), Name = "红烧肉", Portion = "约5块", Calories = 470, Warning = "脂肪含量偏高", SortOrder = 2 });