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/AI/AgentHandlers/medication_agent_handler.cs

@@ -71,8 +71,8 @@ public static class MedicationAgentHandler
             Name = name, Dosage = dosage, Frequency = frequency,
             TimeOfDay = times.Count > 0 ? times : [new TimeOnly(8, 0)],
             Source = MedicationSource.AiEntry, IsActive = true,
-            StartDate = DateOnly.TryParse(startDateStr, out var parsedDate) ? parsedDate : DateOnly.FromDateTime(DateTime.Now),
-            EndDate = durationDays > 0 ? DateOnly.FromDateTime(DateTime.Now).AddDays(durationDays) : null,
+            StartDate = DateOnly.TryParse(startDateStr, out var parsedDate) ? parsedDate : DateOnly.FromDateTime(DateTime.UtcNow.AddHours(8)),
+            EndDate = durationDays > 0 ? DateOnly.FromDateTime(DateTime.UtcNow.AddHours(8)).AddDays(durationDays) : null,
         };
         db.Medications.Add(med);
         await db.SaveChangesAsync();
@@ -100,7 +100,7 @@ public static class MedicationAgentHandler
         db.MedicationLogs.Add(new MedicationLog
         {
             Id = Guid.NewGuid(), MedicationId = medId, UserId = userId,
-            Status = MedicationLogStatus.Taken, ScheduledTime = TimeOnly.FromDateTime(DateTime.Now), ConfirmedAt = DateTime.UtcNow,
+            Status = MedicationLogStatus.Taken, ScheduledTime = TimeOnly.FromDateTime(DateTime.UtcNow.AddHours(8)), ConfirmedAt = DateTime.UtcNow,
         });
         await db.SaveChangesAsync();
         return new { success = true };