Generate descriptive TUI thread titles (#40492)

## What changed

- Give unnamed TUI threads an immediate provisional title from the first user message, then replace it asynchronously with a normalized generated title.
- Preserve manual renames by applying a generated title only while the provisional title is still current, and keep automatic rename notifications out of the transcript.
- Run title generation in a bounded ephemeral structured request that preserves custom permission profiles, otherwise uses read-only access, and disables tools and MCP servers.

## Testing

- Cover prompt and response bounds, Unicode-safe truncation, title normalization, manual-rename races, silent automatic updates, permission preservation, and structured-response failures.

GitOrigin-RevId: 7ed73522f4f6c65a005f65f3a903974d8419e312

codex-rs/tui/src/chatwidget.rs

@@ -667,6 +667,7 @@ pub(crate) struct ChatWidget {
     pet_image_support_override: Option<crate::pets::PetImageSupport>,
     thread_id: Option<ThreadId>,
     thread_name: Option<String>,
+    pending_automatic_thread_names: HashSet<String>,
     thread_rename_block_message: Option<String>,
     active_side_conversation: bool,
     blocks_direct_input: bool,