Conversation naming (#8991)

Session renaming:
- `/rename my_session`
- `/rename` without arg and passing an argument in `customViewPrompt`
- AppExitInfo shows resume hint using the session name if set instead of
uuid, defaults to uuid if not set
- Names are stored in `CODEX_HOME/sessions.jsonl`

Session resuming:
- codex resume <name> lookup for `CODEX_HOME/sessions.jsonl` first entry
matching the name and resumes the session

---------

Co-authored-by: jif-oai <jif@openai.com>

codex-rs/exec/tests/event_processor_with_json_output.rs

@@ -88,6 +88,7 @@ fn session_configured_produces_thread_started_event() {
         EventMsg::SessionConfigured(SessionConfiguredEvent {
             session_id,
             forked_from_id: None,
+            thread_name: None,
             model: "codex-mini-latest".to_string(),
             model_provider_id: "test-provider".to_string(),
             approval_policy: AskForApproval::Never,