fix: preserve ReasoningContent in toolloop for thinking models

When using thinking models (e.g., Kimi K2.5), the API requires
all assistant messages with tool calls to include reasoning_content.
This field was missing in RunToolLoop, causing subagent failures with
the error: 已启用思考功能，但索引2处的助手工具调用消息中缺少推理内容

Aligns toolloop.go with the existing handling in agent/loop.go.

pkg/tools/toolloop.go

@@ -97,8 +97,9 @@ func RunToolLoop(ctx context.Context, config ToolLoopConfig, messages []provider
 
 		// 6. Build assistant message with tool calls
 		assistantMsg := providers.Message{
-			Role:    "assistant",
-			Content: response.Content,
+			Role:             "assistant",
+			Content:          response.Content,
+			ReasoningContent: response.ReasoningContent, // Preserve for thinking models (e.g., GLM-Z1)
 		}
 		for _, tc := range response.ToolCalls {
 			argumentsJSON, _ := json.Marshal(tc.Arguments)