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/widgets/ai_content.dart

@@ -49,17 +49,17 @@ class AiMarkdownView extends StatelessWidget {
         p: AppTextStyles.chatBody,
         a: AppTextStyles.chatBody.copyWith(
           color: AppColors.primary,
-          fontWeight: FontWeight.w800,
+          fontWeight: FontWeight.w600,
           decoration: TextDecoration.underline,
           decorationColor: AppColors.primary,
         ),
-        strong: AppTextStyles.chatBody.copyWith(fontWeight: FontWeight.w800),
+        strong: AppTextStyles.chatBody.copyWith(fontWeight: FontWeight.w600),
         h1: AppTextStyles.chatTitle.copyWith(fontSize: 20),
         h2: AppTextStyles.chatTitle.copyWith(fontSize: 20),
         h3: AppTextStyles.chatTitle.copyWith(fontSize: 19),
         listBullet: AppTextStyles.chatBody.copyWith(
           fontSize: 21,
-          fontWeight: FontWeight.w900,
+          fontWeight: FontWeight.w700,
         ),
         listBulletPadding: const EdgeInsets.only(right: 8),
         blockquote: AppTextStyles.chatBody.copyWith(