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/lib/core/app_theme.dart

@@ -678,7 +678,7 @@ class AppTheme {
       surfaceTintColor: Colors.transparent,
       titleTextStyle: TextStyle(
         fontSize: 20,
-        fontWeight: FontWeight.w800,
+        fontWeight: FontWeight.w700,
         color: text,
       ),
       toolbarHeight: 52,
@@ -724,7 +724,7 @@ class AppTheme {
         foregroundColor: Colors.white,
         minimumSize: const Size(double.infinity, 50),
         shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(rLg)),
-        textStyle: const TextStyle(fontSize: 16, fontWeight: FontWeight.w700),
+        textStyle: const TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
         elevation: 0,
       ),
     ),
@@ -753,12 +753,12 @@ class AppTheme {
     textTheme: const TextTheme(
       headlineLarge: TextStyle(
         fontSize: 24,
-        fontWeight: FontWeight.w800,
+        fontWeight: FontWeight.w700,
         color: text,
       ),
       titleLarge: TextStyle(
         fontSize: 18,
-        fontWeight: FontWeight.w700,
+        fontWeight: FontWeight.w600,
         color: text,
       ),
       titleMedium: TextStyle(