chore: 清理废弃代码和 lint 警告

- 删除旧的 _chip 方法（服药次数改用滚轮后遗留）
- 移除多余的 ! 非空断言

health_app/lib/pages/medication/medication_edit_page.dart

@@ -308,25 +308,6 @@ class _MedicationEditPageState extends ConsumerState<MedicationEditPage> {
           ),
         ],
       );
-  Widget _chip(String label, bool sel, VoidCallback onTap) => GestureDetector(
-    onTap: onTap,
-    child: Container(
-      padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
-      decoration: BoxDecoration(
-        color: sel ? Colors.white : AppColors.cardInner,
-        borderRadius: BorderRadius.circular(16),
-        border: sel ? Border.all(color: AppColors.primary, width: 1.5) : null,
-      ),
-      child: Text(
-        label,
-        style: TextStyle(
-          fontSize: 16,
-          color: sel ? AppColors.primary : AppColors.textSecondary,
-          fontWeight: FontWeight.w500,
-        ),
-      ),
-    ),
-  );
   Widget _dateField(String label, DateTime val, ValueChanged<DateTime> cb) =>
       Column(
         crossAxisAlignment: CrossAxisAlignment.start,