refactor(session): 清理代码 & RunnableConfig 传 sessionId

- AgentLoggingHook 改为从 config.metadata 读取 sessionId（线程安全）
- 移除 AgentLoggingHook 调试用的 metadata 日志
- TokenTrackingChatModel 日志降为 debug
- SessionContextHolder 移除未使用的 setAgentName/getAgentName
- ChatService 清理无用 import
- 修复 stream 路径下 ThreadLocal NPE

src/main/java/com/superbiz/agent/hook/TokenTrackingChatModel.java

@@ -1,5 +1,7 @@
 package com.superbiz.agent.hook;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.ai.chat.model.ChatModel;
 import org.springframework.ai.chat.model.ChatResponse;
 import org.springframework.ai.chat.prompt.Prompt;
@@ -11,6 +13,8 @@ import reactor.core.publisher.Flux;
  */
 public class TokenTrackingChatModel implements ChatModel {
 
+    private static final Logger log = LoggerFactory.getLogger(TokenTrackingChatModel.class);
+
     private final ChatModel delegate;
 
     public TokenTrackingChatModel(ChatModel delegate) {
@@ -31,15 +35,16 @@ public class TokenTrackingChatModel implements ChatModel {
 
     private void captureTokenUsage(ChatResponse response) {
         try {
-            if (response.getMetadata() != null && response.getMetadata().getUsage() != null) {
-                var usage = response.getMetadata().getUsage();
-                Integer total = usage.getTotalTokens();
-                if (total != null && total > 0) {
-                    TokenUsageHolder.set(total);
-                }
+            if (response.getMetadata() == null || response.getMetadata().getUsage() == null) {
+                return;
+            }
+            var usage = response.getMetadata().getUsage();
+            Integer total = usage.getTotalTokens();
+            if (total != null && total > 0) {
+                TokenUsageHolder.set(total);
             }
         } catch (Exception e) {
-            // 不中断模型调用
+            log.debug("捕获 token 用量失败", e);
         }
     }
 }