tui2: copy selection dismisses highlight (#8718)

Clicking the transcript copy pill or pressing the copy shortcut now
copies the selected transcript text and clears the highlight.

Show transient footer feedback ("Copied"/"Copy failed") after a copy
attempt, with logic in transcript_copy_action to keep app.rs smaller and
closer to tui for long-term diffs.

Update footer snapshots and add tiny unit tests for feedback expiry.


https://github.com/user-attachments/assets/c36c8163-11c5-476b-b388-e6fbe0ff6034

codex-rs/tui2/src/chatwidget.rs

@@ -3096,12 +3096,14 @@ impl ChatWidget {
         selection_active: bool,
         scroll_position: Option<(usize, usize)>,
         copy_selection_key: crate::key_hint::KeyBinding,
+        copy_feedback: Option<crate::transcript_copy_action::TranscriptCopyFeedback>,
     ) {
         self.bottom_pane.set_transcript_ui_state(
             scrolled,
             selection_active,
             scroll_position,
             copy_selection_key,
+            copy_feedback,
         );
     }