升级到v1.3.0：新增auto推理模式和完善推理级别文档

主要功能更新：
- 新增auto推理级别，完全遵循客户端原始请求参数
- 支持五档推理级别：auto/off/low/medium/high
- auto模式零干预：不修改推理字段和anthropic-beta头
- 除gpt-5-codex外，所有模型默认设为auto模式

文档完善：
- 更新核心功能说明，突出智能推理级别控制
- 新增auto推理模式详细说明和使用场景
- 添加推理级别对比表格和配置示例
- 增强FAQ部分，分场景解答推理相关问题
- 提供OpenAI和Anthropic模型字段对应关系

技术实现：
- 更新getModelReasoning函数支持auto选项
- 完善所有transformer的auto模式处理逻辑
- 优化routes.js中直接转发端点的auto支持
- 确保auto模式下头信息和请求体完全透传

transformers/request-openai.js

@@ -94,14 +94,20 @@ export function transformToOpenAI(openaiRequest) {
 
   // Handle reasoning field based on model configuration
   const reasoningLevel = getModelReasoning(openaiRequest.model);
-  if (reasoningLevel) {
-    // Add reasoning field based on model configuration
+  if (reasoningLevel === 'auto') {
+    // Auto mode: preserve original request's reasoning field exactly as-is
+    if (openaiRequest.reasoning !== undefined) {
+      targetRequest.reasoning = openaiRequest.reasoning;
+    }
+    // If original request has no reasoning field, don't add one
+  } else if (reasoningLevel && ['low', 'medium', 'high'].includes(reasoningLevel)) {
+    // Specific level: override with model configuration
     targetRequest.reasoning = {
       effort: reasoningLevel,
       summary: 'auto'
     };
   } else {
-    // If reasoning is off or invalid, explicitly remove reasoning field
+    // Off or invalid: explicitly remove reasoning field
     // This ensures any reasoning field from the original request is deleted
     delete targetRequest.reasoning;
   }