添加会话级固定预设

Co-Authored-By: Claude <noreply@anthropic.com>

templates/chat.html

@@ -771,7 +771,12 @@ async function loadConversationList() {
 }
 
 async function createConversation() {
-  const res = await fetch('/api/conversations', { method: 'POST' });
+  const preset = getPresetPrompt();
+  const res = await fetch('/api/conversations', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ preset_prompt: preset }),
+  });
   if (!res.ok) {
     const err = await res.json().catch(() => ({ error: '创建对话失败' }));
     throw new Error(err.error || '创建对话失败');
@@ -1075,7 +1080,6 @@ async function sendMessage() {
 
   try {
     if (!currentConvId) {
-      ensurePresetLoaded();
       const conv = await createConversation();
       currentConvId = conv.id;
       await loadConversationList();