Fix TUI input queue handling during MCP startup (#35957)

## Why

Pending MCP server startup can outlive an agent turn. Treating its shared
running indicator as an active user turn prevents queued follow-ups and slash
commands from advancing after the turn completes.

## What changed

- Allow the input queue to drain while only MCP startup remains active.
- Keep queued input blocked while a review, foreground shell command, or
  compaction is pending or running.
- Resume queue draining after session-selection flows close.

## Testing

Add TUI tests covering queued follow-ups, slash commands, reviews, shell
commands, and compaction while MCP startup is pending.

GitOrigin-RevId: f5684f61c32e3728ff71cf222f0486df637dc3a5

codex-rs/tui/src/chatwidget.rs

@@ -1770,6 +1770,14 @@ impl ChatWidget {
     }
 
     pub(crate) fn prepare_local_op_submission(&mut self, op: &AppCommand) {
+        if matches!(
+            op,
+            AppCommand::Compact
+                | AppCommand::Review { .. }
+                | AppCommand::RunUserShellCommand { .. }
+        ) {
+            self.input_queue.user_turn_pending_start = true;
+        }
         if matches!(op, AppCommand::Interrupt) && self.turn_lifecycle.agent_turn_running {
             if let Some(controller) = self.stream_controller.as_mut() {
                 controller.clear_queue();