fix transcript lines being added to diff view (#2721)

This fixes a bug where if you ran /diff while at turn was running,
transcript lines would be added to the end of the diff view. Also,
refactor to make this kind of issue less likely in future.

codex-rs/tui/src/lib.rs

@@ -46,6 +46,7 @@ pub mod live_wrap;
 mod markdown;
 mod markdown_stream;
 pub mod onboarding;
+mod pager_overlay;
 mod render;
 mod session_log;
 mod shimmer;
@@ -53,7 +54,6 @@ mod slash_command;
 mod status_indicator_widget;
 mod streaming;
 mod text_formatting;
-mod transcript_app;
 mod tui;
 mod user_approval_widget;