Allow naming sessions with /new and /clear (#34605)

## What changed

- Accept an optional session name after `/new` or `/clear`.
- Set the requested name through the app server when starting the new thread and update the attached session with that name.
- Report naming failures in the chat while still attaching the newly created thread.

## Testing

- Cover named `/new` and `/clear` dispatch, app-server name persistence, and the existing unnamed `/clear` behavior.

GitOrigin-RevId: 570886abb4af522123f0693ce05d2415e1c0d902

codex-rs/tui/src/app_event.rs

@@ -235,8 +235,10 @@ pub(crate) enum AppEvent {
         log_id: u64,
     },
 
-    /// Start a new session.
-    NewSession,
+    /// Start a new session, optionally assigning it a name.
+    NewSession {
+        name: Option<String>,
+    },
 
     /// Result of the fresh startup thread that is attached after the input UI is live.
     StartupThreadStarted {
@@ -245,7 +247,9 @@ pub(crate) enum AppEvent {
 
     /// Clear the terminal UI (screen + scrollback), start a fresh session, and keep the
     /// previous chat resumable.
-    ClearUi,
+    ClearUi {
+        name: Option<String>,
+    },
 
     /// Re-render the transcript using the selected scrollback rendering mode.
     RawOutputModeChanged {