fix: 修复守护进程日志中文截取 panic

- daemon.rs: 使用字符索引替代字节索引截取日志文本
- agents.md: 添加踩坑记录

src/daemon.rs

@@ -330,8 +330,9 @@ async fn process_tts_request(request: DaemonRequest) -> Result<String> {
     let format = request.format.unwrap_or_else(|| "wav".to_string());
     let style = request.style;
     
+    let text_preview: String = text.chars().take(50).collect();
     write_log(&format!("处理 TTS: text={}, voice={}, format={}, style={:?}", 
-        &text[..text.len().min(50)], voice, format, style))?;
+        text_preview, voice, format, style))?;
     
     // 处理风格标签
     let mut final_text = text.clone();