feat: 后台管理页全量重构 + backoffice 共享模块 + 启动脚本优化

## 后台管理页重构
- admin 端: add_doctor / doctors / home / patients 四页重构
- doctor 端: consultations / dashboard / followup_edit / followups / home / patient_detail / patients / profile / report_detail / reports / settings 十一页重构
- 新增 backoffice 共享模块: backoffice_refresh_providers + backoffice_formatters + backoffice_ui

## 后端
- AdminService 增强(分页/搜索/统计)
- doctor_endpoints 微调
- appsettings.Development 调整
- 新增 admin_service_tests

## 前端其他
- 今日健康卡片 taskRow 行高 5->7(每行 44->48px)
- 健康仪表盘配色定 #4FACFE 纯色蓝
- admin_drawer / doctor_drawer 微调
- api_client IP 适配

## 启动脚本
- start-dev.bat: 加后端就绪检测(轮询 openapi 端点, 最多等 30s)

## 清理
- 删除旧品牌图(agent_welcome_abstract / login_background_v1)
- 删除 app_status_badge 组件
- 删除旧 HANDOFF 文档, 新增 07-17 版

## 测试
- 新增 backoffice_formatters / backoffice_refresh / backoffice_ui 三个测试
- app_router_test 扩展

health_app/lib/widgets/health_drawer.dart

@@ -214,9 +214,9 @@ class _HealthDashboard extends StatelessWidget {
       ),
       titleColor: Colors.white,
       backgroundGradient: const LinearGradient(
-        begin: Alignment.centerLeft,
-        end: Alignment.centerRight,
-        colors: [Color(0xFF4FACFE), Color(0xFF00F2FE)],
+        begin: Alignment.topCenter,
+        end: Alignment.bottomCenter,
+        colors: [Color(0xFF89F7FE), Color(0xFF66A6FF)],
       ),
       child: latestHealth.when(
         data: (data) => _DashboardMetrics(data: data, ref: ref),