Migrate tui to use UserTurn (#9497)

- `tui/` and `tui2/` submit `Op::UserTurn` and own full turn context
(cwd/approval/sandbox/model/etc.).
- `Op::UserInput` is documented as legacy in `codex-protocol` (doc-only;
no `#[deprecated]` to avoid `-D warnings` fallout).
- Remove obsolete `#[allow(deprecated)]` and the unused `ConversationId`
alias/re-export.

codex-rs/tui/src/chatwidget/tests.rs

@@ -457,7 +457,6 @@ fn next_submit_op(op_rx: &mut tokio::sync::mpsc::UnboundedReceiver<Op>) -> Op {
     loop {
         match op_rx.try_recv() {
             Ok(op @ Op::UserTurn { .. }) => return op,
-            Ok(op @ Op::UserInput { .. }) => return op,
             Ok(_) => continue,
             Err(TryRecvError::Empty) => panic!("expected a submit op but queue was empty"),
             Err(TryRecvError::Disconnected) => panic!("expected submit op but channel closed"),