feat: 健康仪表盘配色调整 + 登录页品牌升级 + iOS 配置 + 隐私文案修订 + 文档清理

## UI 配色
- 健康仪表盘: 背景从蓝紫粉三色渐变改为 #4FACFE 纯色蓝, 白字清晰不抢眼
- app_colors / app_design_tokens / app_theme: 配色体系微调
- 多个 widget 和页面跟随配色更新(health_drawer/admin_drawer/doctor_drawer/enterprise_widgets 等)

## 登录页品牌升级
- 新增品牌素材: drawer_background_v2 / login_background_v2 / health_login_character_transparent
- login_page 重构, 接入新品牌视觉
- app.dart 启动流程调整

## iOS / Android 配置
- Info.plist: 权限描述调整
- AppIcon / LaunchImage: 资源更新
- AndroidManifest: 权限微调

## 隐私文案修订
- privacy.html: 蓝牙设备描述调整为"标准蓝牙血压服务", 移除未上线设备类型表述
- terms.html: 移除"在线医生咨询"相关条款, 服务范围收窄

## 通知中心
- notification_center_page: 重构通知项布局

## 其他
- 删除已完成的计划/spec 文档(ui-system-first-pass / apple-sign-in / secondary-page-color-refresh / notification-preferences-design / ui-design-system)
- 新增 native_navigation_test
- 新增 HANDOFF 交接文档
- home_message_order_test 更新
- .gitignore 调整

health_app/test/native_navigation_test.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:health_app/app.dart';
+import 'package:health_app/core/navigation_provider.dart';
+import 'package:health_app/providers/auth_provider.dart';
+
+class _TestAuthNotifier extends AuthNotifier {
+  @override
+  AuthState build() => const AuthState(isLoggedIn: false, isLoading: false);
+}
+
+void main() {
+  testWidgets('native navigator pop keeps the app route stack in sync', (
+    tester,
+  ) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    addTearDown(() => debugDefaultTargetPlatformOverride = null);
+
+    final container = ProviderContainer(
+      overrides: [authProvider.overrideWith(_TestAuthNotifier.new)],
+    );
+    addTearDown(container.dispose);
+
+    await tester.pumpWidget(
+      UncontrolledProviderScope(container: container, child: const HealthApp()),
+    );
+    await tester.pump();
+
+    container
+        .read(routeStackProvider.notifier)
+        .push('staticText', params: const {'type': 'privacy'});
+    await tester.pumpAndSettle();
+
+    final navigators = tester
+        .stateList<NavigatorState>(find.byType(Navigator))
+        .toList();
+    expect(navigators.length, greaterThanOrEqualTo(2));
+    expect(navigators.last.canPop(), isTrue);
+    final route = ModalRoute.of(tester.element(find.text('隐私协议').first));
+    expect(route, isA<PageRoute<void>>());
+    expect((route! as PageRoute<void>).popGestureEnabled, isTrue);
+
+    await tester.dragFrom(const Offset(5, 100), const Offset(500, 0));
+    await tester.pump(const Duration(milliseconds: 351));
+    await tester.pumpAndSettle();
+
+    debugDefaultTargetPlatformOverride = null;
+    expect(container.read(routeStackProvider).length, 1);
+  });
+}