fix(proxy): preserve URL query/fragment and improve error handling

Extract shared URL utilities to handle query strings and fragments correctly.
Add race condition fix for URL preview, improve proxy toggle error feedback,
and support Codex chat format proxy endpoint.

src-tauri/src/proxy/mod.rs

@@ -24,6 +24,7 @@ pub mod session;
 pub mod thinking_rectifier;
 pub(crate) mod types;
 pub mod url_builder;
+pub(crate) mod url_utils;
 pub mod usage;
 
 // 公开导出给外部使用（commands, services等模块需要）