Add log-to-file feature with background writer

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

crates/xserial-gui/src/main.rs

@@ -1,6 +1,7 @@
 mod app;
 mod app_state;
 mod buffers;
+mod logging;
 mod panels;
 mod perf;
 mod shortcuts;