fix: AI Chat 主备双模型 + Sensenova reasoning 兼容

- 数据库模型迁移：删除旧 Opencode/api.qnaigc 配置
- 主模型: Sensenova (sensenova-6.7-flash-lite) ✓
- 备模型: NVIDIA (stepfun-ai/step-3.5-flash) ✓
- aiChat.js 主备切换逻辑：主模型失败自动降级到备模型
- 兼容 Sensenova 的 reasoning 字段（非标准 content）
- API URL 统一补全 /chat/completions 路径

server/src/routes/aiChat.js

@@ -72,71 +72,21 @@ router.post('/ask', userAuthMiddleware, async (req, res) => {
       return ApiResponse.error(res, '问答次数已用完，分享好友可获得更多次数', 403)
     }
     
-    // 获取当前使用的AI模型配置
+    // 获取所有启用的AI模型（用于主备切换）
-    const aiModel = await AIModel.getCurrentModel()
+    const aiModels = await AIModel.getActiveModels()
     
-    let apiUrl, apiKey, modelId, modelConfig
+    if (!aiModels || aiModels.length === 0) {
-    
-    if (aiModel) {
-      // 使用数据库配置的模型
-      apiUrl = aiModel.apiUrl
-      apiKey = aiModel.apiKey
-      modelId = aiModel.modelId
-      modelConfig = aiModel.config
-    } else {
       // 使用环境变量配置的模型
-      apiUrl = process.env.OPENAI_API_URL || 'https://api.openai.com/v1/chat/completions'
+      const envModels = [{
-      apiKey = process.env.OPENAI_API_KEY
+        apiUrl: process.env.OPENAI_API_URL || 'https://api.openai.com/v1/chat/completions',
-      modelId = process.env.OPENAI_MODEL || 'gpt-3.5-turbo'
+        apiKey: process.env.OPENAI_API_KEY,
-      modelConfig = { temperature: 0.7, maxTokens: 800, topP: 1 }
+        modelId: process.env.OPENAI_MODEL || 'gpt-3.5-turbo',
+        config: { temperature: 0.7, maxTokens: 800, topP: 1 }
+      }]
+      return await tryModels(envModels, question, dimension, res, quota)
     }
     
-    // 检查API配置（opencode.ai免费API无需key）
+    return await tryModels(aiModels, question, dimension, res, quota)
-    const needsAuth = apiKey && apiKey !== 'sk-dummy' && apiKey !== '***'
-    
-    // 构建系统提示词
-    const systemPrompt = getSystemPromptByDimension(dimension)
-    
-    // 构建请求头
-    const headers = {
-      'Content-Type': 'application/json'
-    }
-    if (needsAuth) {
-      headers['Authorization'] = `Bearer ${apiKey}`
-    }
-    
-    // 调用AI API
-    const response = await fetch(apiUrl, {
-      method: 'POST',
-      headers,
-      body: JSON.stringify({
-        model: modelId,
-        messages: [
-          { role: 'system', content: systemPrompt },
-          { role: 'user', content: question }
-        ],
-        temperature: modelConfig.temperature || 0.7,
-        max_tokens: modelConfig.maxTokens || 800,
-        top_p: modelConfig.topP || 1
-      })
-    })
-    
-    if (!response.ok) {
-      const errorData = await response.json()
-      logger.error('OpenAI API错误:', errorData)
-      return ApiResponse.error(res, 'AI服务响应异常', 500)
-    }
-    
-    const data = await response.json()
-    const answer = data.choices[0].message.content
-    
-    // 扣除一次使用次数
-    await quota.useQuota()
-    
-    return ApiResponse.success(res, {
-      answer,
-      remainingQuota: quota.getRemainingQuota()
-    })
     
   } catch (error) {
     logger.error('AI问答失败:', error)
@@ -144,6 +94,81 @@ router.post('/ask', userAuthMiddleware, async (req, res) => {
   }
 })
 
+/**
+ * 遍历模型列表尝试问答（主备切换）
+ */
+async function tryModels(models, question, dimension, res, quota) {
+  const systemPrompt = getSystemPromptByDimension(dimension)
+  let lastError = null
+  
+  for (const model of models) {
+    try {
+      const apiUrl = model.apiUrl
+      const apiKey = model.apiKey
+      const modelId = model.modelId
+      const modelConfig = model.config || {}
+      
+      // 检查是否需要 Authorization（免费/无需key的API跳过）
+      const needsAuth = apiKey && apiKey !== 'sk-dummy' && apiKey !== '***'
+      
+      // 构建请求头
+      const headers = { 'Content-Type': 'application/json' }
+      if (needsAuth) {
+        headers['Authorization'] = `Bearer ${apiKey}`
+      }
+      
+      logger.info(`[AI Chat] 尝试模型: ${model.name} (${modelId})`)
+      
+      // 调用AI API
+      const response = await fetch(apiUrl, {
+        method: 'POST',
+        headers,
+        body: JSON.stringify({
+          model: modelId,
+          messages: [
+            { role: 'system', content: systemPrompt },
+            { role: 'user', content: question }
+          ],
+          temperature: modelConfig.temperature || 0.7,
+          max_tokens: modelConfig.maxTokens || 800,
+          top_p: modelConfig.topP || 1
+        })
+      })
+      
+      if (!response.ok) {
+        const errorData = await response.json().catch(() => ({}))
+        logger.warn(`[AI Chat] 模型 ${model.name} 失败:`, response.status, errorData)
+        lastError = { status: response.status, data: errorData }
+        continue // 尝试下一个模型
+      }
+      
+      const data = await response.json()
+      const message = data.choices[0].message
+      // 兼容标准 content 和 sensenova 的 reasoning 字段
+      const answer = message.content || message.reasoning || ''
+      
+      // 扣除一次使用次数
+      await quota.useQuota()
+      
+      logger.info(`[AI Chat] 模型 ${model.name} 回答成功`)
+      
+      return ApiResponse.success(res, {
+        answer,
+        remainingQuota: quota.getRemainingQuota()
+      })
+      
+    } catch (err) {
+      logger.warn(`[AI Chat] 模型 ${model.name} 异常:`, err.message)
+      lastError = { message: err.message }
+      continue // 尝试下一个模型
+    }
+  }
+  
+  // 所有模型都失败了
+  logger.error('所有AI模型均失败:', lastError)
+  return ApiResponse.error(res, 'AI服务暂时不可用，请稍后再试', 500)
+}
+
 /**
  * 分享获得问答次数
  * POST /api/ai-chat/share-gain