Add paste summarization to Codex TUI (#1549)

## Summary
- introduce `Paste` event to avoid per-character paste handling
- collapse large pasted blocks to `[Pasted Content X lines]`
- store the real text so submission still includes it
- wire paste handling through `App`, `ChatWidget`, `BottomPane`, and
`ChatComposer`

## Testing
- `cargo test -p codex-tui`


------
https://chatgpt.com/codex/tasks/task_i_6871e24abf80832184d1f3ca0c61a5ee


https://github.com/user-attachments/assets/eda7412f-da30-4474-9f7c-96b49d48fbf8

codex-rs/tui/src/app.rs

@@ -98,21 +98,7 @@ impl<'a> App<'a> {
                             scroll_event_helper.scroll_down();
                         }
                         crossterm::event::Event::Paste(pasted) => {
-                            use crossterm::event::KeyModifiers;
-
-                            for ch in pasted.chars() {
-                                let key_event = match ch {
-                                    '\n' | '\r' => {
-                                        // Represent newline as <Shift+Enter> so that the bottom
-                                        // pane treats it as a literal newline instead of a submit
-                                        // action (submission is only triggered on Enter *without*
-                                        // any modifiers).
-                                        KeyEvent::new(KeyCode::Enter, KeyModifiers::SHIFT)
-                                    }
-                                    _ => KeyEvent::new(KeyCode::Char(ch), KeyModifiers::empty()),
-                                };
-                                app_event_tx.send(AppEvent::KeyEvent(key_event));
-                            }
+                            app_event_tx.send(AppEvent::Paste(pasted));
                         }
                         _ => {
                             // Ignore any other events.
@@ -223,6 +209,9 @@ impl<'a> App<'a> {
                 AppEvent::Scroll(scroll_delta) => {
                     self.dispatch_scroll_event(scroll_delta);
                 }
+                AppEvent::Paste(text) => {
+                    self.dispatch_paste_event(text);
+                }
                 AppEvent::CodexEvent(event) => {
                     self.dispatch_codex_event(event);
                 }
@@ -343,6 +332,13 @@ impl<'a> App<'a> {
         }
     }
 
+    fn dispatch_paste_event(&mut self, pasted: String) {
+        match &mut self.app_state {
+            AppState::Chat { widget } => widget.handle_paste(pasted),
+            AppState::Login { .. } | AppState::GitWarning { .. } => {}
+        }
+    }
+
     fn dispatch_scroll_event(&mut self, scroll_delta: i32) {
         match &mut self.app_state {
             AppState::Chat { widget } => widget.handle_scroll_delta(scroll_delta),