Compact successful command activity in the TUI (#38921)

## What changed

- Group consecutive successful agent and unified-exec startup commands into a compact `Ran N commands` entry while preserving their full transcript.
- Flush command groups at interaction boundaries, after failures, and after 32 completed commands. Keep manual shell commands and failed or declined commands visible.
- Apply the same grouping rules when replaying thread history without duplicating command starts or disturbing unrelated active commands.

## Testing

- Add TUI coverage for live and replayed grouping, transcript preservation, failures, overlapping commands, group limits, and interaction boundaries.

GitOrigin-RevId: d6602a20201644012fcff3d6cecf4690024383a9

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

@@ -145,6 +145,7 @@ impl ChatWidget {
     }
 
     pub(super) fn dispatch_command(&mut self, cmd: SlashCommand) {
+        self.flush_completed_command_activity();
         if !self.ensure_slash_command_allowed_in_side_conversation(cmd) {
             return;
         }