feat: 饮食记录逻辑重构 + 通知管理分隔线修复 + 多页面 UI 调整

- 饮食: 新增 DietCommentaryPolicy + diet_record_logic, 饮食记录逻辑抽取复用
- 通知管理: 分隔线改为仿通知中心样式, 跳过图标区域只留文字下方
- 侧边栏: 对话记录操作栏浮层修复 + 常用功能间距收紧
- 智能体: 欢迎卡片去 400ms 延迟 + 胶囊去阴影
- 后端: AI 会话仓库新增方法 + 饮食评论策略 + 健康记录规则调整
- 其他: api_client IP 适配 + 多页面 UI 微调 + 新增测试

health_app/lib/widgets/app_gradient_widgets.dart

@@ -0,0 +1,93 @@
+import 'package:flutter/material.dart';
+
+import '../core/app_colors.dart';
+
+class AppGradientText extends StatelessWidget {
+  final String text;
+  final TextStyle style;
+  final Gradient gradient;
+  final TextAlign? textAlign;
+
+  const AppGradientText(
+    this.text, {
+    super.key,
+    required this.style,
+    this.gradient = AppColors.primaryGradient,
+    this.textAlign,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return ShaderMask(
+      shaderCallback: gradient.createShader,
+      blendMode: BlendMode.srcIn,
+      child: Text(
+        text,
+        textAlign: textAlign,
+        style: style.copyWith(color: Colors.white),
+      ),
+    );
+  }
+}
+
+class AppGradientIcon extends StatelessWidget {
+  final IconData icon;
+  final double size;
+  final Gradient gradient;
+
+  const AppGradientIcon({
+    super.key,
+    required this.icon,
+    required this.size,
+    this.gradient = AppColors.primaryGradient,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return ShaderMask(
+      shaderCallback: gradient.createShader,
+      blendMode: BlendMode.srcIn,
+      child: Icon(icon, size: size, color: Colors.white),
+    );
+  }
+}
+
+class AppGradientOutlineButton extends StatelessWidget {
+  final String label;
+  final VoidCallback onTap;
+  final Gradient gradient;
+
+  const AppGradientOutlineButton({
+    super.key,
+    required this.label,
+    required this.onTap,
+    this.gradient = AppColors.primaryGradient,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      onTap: onTap,
+      child: Container(
+        height: 50,
+        decoration: BoxDecoration(
+          gradient: gradient,
+          borderRadius: BorderRadius.circular(18),
+        ),
+        padding: const EdgeInsets.all(1.2),
+        child: Container(
+          alignment: Alignment.center,
+          decoration: BoxDecoration(
+            color: Colors.white,
+            borderRadius: BorderRadius.circular(17),
+          ),
+          child: AppGradientText(
+            label,
+            gradient: gradient,
+            style: const TextStyle(fontSize: 16, fontWeight: FontWeight.w800),
+          ),
+        ),
+      ),
+    );
+  }
+}