fix: 支援不接受 system role 的模型（DeepSeek-R1）

app/llm.js

@@ -16,9 +16,16 @@ export async function chat(systemPrompt, userContent) {
   };
   if (provider === 'claude') headers['anthropic-version'] = '2023-06-01';
 
+  // 部分模型（如 DeepSeek-R1）不支援 system role，改合併到 user message
+  const NO_SYSTEM_ROLE_MODELS = ['deepseek-ai/deepseek-r1', 'deepseek-r1'];
+  const isNoSystemRole = NO_SYSTEM_ROLE_MODELS.some(m => model.toLowerCase().includes(m.toLowerCase()));
+  const messages = isNoSystemRole
+    ? [{ role: 'user', content: `${systemPrompt}\n\n${userContent}` }]
+    : [{ role: 'system', content: systemPrompt }, { role: 'user', content: userContent }];
+
   const resp = await axios.post(
     `${baseURL.replace(/\/$/, '')}/chat/completions`,
-    { model, messages: [{ role: 'system', content: systemPrompt }, { role: 'user', content: userContent }], temperature: 0.2 },
+    { model, messages, temperature: 0.2 },
     { headers, timeout: 120000, httpsAgent }
   );
   return resp.data.choices[0].message.content;