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/test/backoffice_formatters_test.dart

@@ -0,0 +1,21 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:health_app/utils/backoffice_formatters.dart';
+
+void main() {
+  test('formats report time without assuming a minimum string length', () {
+    expect(formatBackofficeDateTime(null), '时间未知');
+    expect(formatBackofficeDateTime(''), '时间未知');
+    expect(formatBackofficeDateTime('2026-07-17'), '2026-07-17');
+    expect(
+      formatBackofficeDateTime('2026-07-17T10:20:30Z'),
+      '2026-07-17 10:20',
+    );
+  });
+
+  test('builds a safe avatar initial for empty or missing names', () {
+    expect(backofficeInitial(null), '?');
+    expect(backofficeInitial(''), '?');
+    expect(backofficeInitial('  '), '?');
+    expect(backofficeInitial('小脉'), '小');
+  });
+}