feat: UI 清新风全面改造 — 朝露主题 + shadcn_ui + 全局字号放大

- 全新"朝露"主题：深青绿主色(#2D6A4F)，暖白底，完整设计Token
- 引入 shadcn_ui 组件库，MaterialApp 注入 ShadTheme
- 新增 4 个公共组件：AppCard、AppMenuItem、AppEmptyState、AppTabChip
- 全面消除硬编码颜色，统一使用 AppTheme Token
- 全局字号 +3~4pt，图标等比放大 +3px
- home/medication/profile/settings/login 等核心页面重写
- 路由和功能逻辑零改动

health_app/lib/widgets/app_card.dart

@@ -0,0 +1,46 @@
+import 'package:flutter/material.dart';
+import 'package:shadcn_ui/shadcn_ui.dart';
+import '../core/app_theme.dart';
+
+/// 统一样式的清新卡片
+class AppCard extends StatelessWidget {
+  final Widget child;
+  final EdgeInsetsGeometry? padding;
+  final EdgeInsetsGeometry? margin;
+  final VoidCallback? onTap;
+  final Color? backgroundColor;
+  final BorderRadius? borderRadius;
+
+  const AppCard({
+    super.key,
+    required this.child,
+    this.padding = const EdgeInsets.all(AppTheme.sLg),
+    this.margin,
+    this.onTap,
+    this.backgroundColor,
+    this.borderRadius,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = ShadTheme.of(context);
+    final card = Container(
+      margin: margin ?? const EdgeInsets.symmetric(horizontal: AppTheme.sLg, vertical: AppTheme.sSm),
+      padding: padding,
+      decoration: BoxDecoration(
+        color: backgroundColor ?? theme.colorScheme.card,
+        borderRadius: borderRadius ?? BorderRadius.circular(AppTheme.rMd),
+        boxShadow: [AppTheme.shadowLight],
+      ),
+      child: child,
+    );
+
+    if (onTap != null) {
+      return GestureDetector(
+        onTap: onTap,
+        child: card,
+      );
+    }
+    return card;
+  }
+}