feat: 添加vLLM适配器、修复SSE流式输出和中间件问题

- 新增 vLLM 适配器 (internal/adapter/vllm.go)，支持 OpenAI 兼容 API
- 修复 responseWriter 未实现 http.Flusher 导致 SSE 流式输出 500 错误
- 调整中间件顺序：BodyLimit 移至 Auth 之前，提前拒绝超大请求
- BodyLimit 增强：检查 Content-Length header
- 导出 Server.Authenticator() 方法供测试使用
- 配置更新：使用本地 deepseek-r1:1.5b 模型，新增 vllm-chat 逻辑模型
- 修复 handlers.go 中未使用的 target 参数 lint 警告

internal/server/handlers.go

@@ -122,7 +122,7 @@ func (s *Server) handleChatCompletions(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-func (s *Server) handleStreaming(w http.ResponseWriter, r *http.Request, adapterInst adapter.ModelAdapter, req *adapter.ChatRequest, tk *task.Task, requestID string, target *router.ModelTarget, logicalModel string) {
+func (s *Server) handleStreaming(w http.ResponseWriter, r *http.Request, adapterInst adapter.ModelAdapter, req *adapter.ChatRequest, tk *task.Task, requestID string, _ *router.ModelTarget, logicalModel string) {
 	sse := handler.NewSSEWriter(w)
 	if sse == nil {
 		s.scheduler.Complete(tk.ID)
@@ -158,7 +158,7 @@ func (s *Server) handleStreaming(w http.ResponseWriter, r *http.Request, adapter
 	s.metrics.IncRequest("stream_ok")
 }
 
-func (s *Server) handleNonStreaming(w http.ResponseWriter, r *http.Request, adapterInst adapter.ModelAdapter, req *adapter.ChatRequest, tk *task.Task, requestID string, target *router.ModelTarget, logicalModel string) {
+func (s *Server) handleNonStreaming(w http.ResponseWriter, r *http.Request, adapterInst adapter.ModelAdapter, req *adapter.ChatRequest, tk *task.Task, requestID string, _ *router.ModelTarget, logicalModel string) {
 	ctx, cancel := context.WithTimeout(r.Context(), time.Duration(s.cfg.Timeouts.DefaultInferenceMs)*time.Millisecond)
 	defer cancel()
 

internal/server/server.go

@@ -68,6 +68,8 @@ func New(cfg *config.Config, logger *observability.Logger) (*Server, error) {
 			switch mc.Provider {
 			case "ollama":
 				registry.Register(mc.Provider, adapter.NewOllamaAdapter(mc.Endpoint))
+			case "vllm":
+				registry.Register(mc.Provider, adapter.NewVLLMAdapter(mc.Endpoint))
 			}
 			registered[key] = true
 		}