fix: VLM 参数优化 - temperature 0.7, top_p 0.8, 指令放 system+user

- VisionAsync 新增 Temperature=0.7, TopP=0.8
- system prompt 用专业营养识别指令
- userText 用简短"请看图识别食物"配合图片
- 修复重复 prompt 导致 VLM 误读文本的 bug

health_app/lib/widgets/health_drawer.dart

@@ -18,8 +18,8 @@ class HealthDrawer extends ConsumerWidget {
 
     return Drawer(
       child: SafeArea(
-        child: Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
+        child: ListView(
+          padding: EdgeInsets.zero,
           children: [
             // 用户信息
             Container(
@@ -75,13 +75,15 @@ class HealthDrawer extends ConsumerWidget {
                 TextButton(onPressed: () => ref.invalidate(conversationListProvider), child: const Text('刷新', style: TextStyle(fontSize: 12, color: Color(0xFF635BFF)))),
               ]),
             ),
-            Expanded(
+            SizedBox(
+              height: 200,
               child: conversations.when(
                 data: (items) {
                   if (items.isEmpty) {
                     return const Center(child: Text('暂无历史对话', style: TextStyle(color: Color(0xFF999999), fontSize: 14)));
                   }
                   return ListView.builder(
+                    shrinkWrap: true,
                     padding: const EdgeInsets.symmetric(horizontal: 8),
                     itemCount: items.length,
                     itemBuilder: (ctx, i) => _ConversationItem(item: items[i], ref: ref),
@@ -162,8 +164,8 @@ class _ConversationItem extends ConsumerWidget {
           ),
           child: Icon(_getAgentIcon(item.agent), size: 18, color: const Color(0xFF635BFF)),
         ),
-        title: Text(item.title, style: const TextStyle(fontSize: 14, fontWeight: FontWeight.w500)),
-        subtitle: Text(item.lastMessage, style: TextStyle(fontSize: 12, color: Colors.grey[500])),
+        title: Text(item.title, maxLines: 1, overflow: TextOverflow.ellipsis, style: const TextStyle(fontSize: 14, fontWeight: FontWeight.w500)),
+        subtitle: Text(item.lastMessage, maxLines: 1, overflow: TextOverflow.ellipsis, style: TextStyle(fontSize: 12, color: Colors.grey[500])),
         trailing: Column(
           mainAxisAlignment: MainAxisAlignment.center,
           children: [