[codex] Move thread naming to app server (#21260)

## Why

Thread names are app-server metadata now, backed by the thread store and
sqlite state database. Keeping a core `SetThreadName` op plus a rollout
`thread_name_updated` event made rename persistence live in the wrong
layer and required historical replay support for an event that new
app-server flows should not write.

## What changed

- Removed `Op::SetThreadName` and `EventMsg::ThreadNameUpdated` from the
core protocol and deleted the core handler path that appended rename
events to rollouts.
- Updated app-server `thread/name/set` so both loaded and unloaded
threads write through thread-store metadata and app-server emits
`thread/name/updated` notifications.
- Updated local thread-store name metadata updates to write sqlite title
metadata and the legacy thread-name index without appending rollout
events.
- Removed state extraction and rollout handling for the deleted
thread-name event.

## Validation

- `cargo test -p codex-app-server thread_name_updated_broadcasts`
- `cargo test -p codex-app-server
thread_name_set_is_reflected_in_read_list_and_resume`
- `cargo test -p codex-thread-store
update_thread_metadata_sets_name_on_active_rollout_and_indexes_name`
- `cargo test -p codex-state`
- `cargo check -p codex-mcp-server -p codex-rollout-trace`
- `just fix -p codex-app-server -p codex-thread-store -p codex-state -p
codex-mcp-server -p codex-rollout-trace`

## Docs

No external documentation update is expected for this internal ownership
change.

codex-rs/app-server/src/request_processors/thread_processor.rs

@@ -405,10 +405,7 @@ impl ThreadRequestProcessor {
         request_id: ConnectionRequestId,
         params: ThreadSetNameParams,
     ) -> Result<Option<ClientResponsePayload>, JSONRPCErrorError> {
-        match self
-            .thread_set_name_response_inner(&request_id, params)
-            .await
-        {
+        match self.thread_set_name_response_inner(params).await {
             Ok((response, notification)) => {
                 self.outgoing
                     .send_response(request_id.clone(), response)
@@ -1335,7 +1332,6 @@ impl ThreadRequestProcessor {
 
     async fn thread_set_name_response_inner(
         &self,
-        request_id: &ConnectionRequestId,
         params: ThreadSetNameParams,
     ) -> Result<(ThreadSetNameResponse, Option<ThreadNameUpdatedNotification>), JSONRPCErrorError>
     {
@@ -1347,13 +1343,6 @@ impl ThreadRequestProcessor {
         };
 
         let _thread_list_state_permit = self.acquire_thread_list_state_permit().await?;
-        if let Ok(thread) = self.thread_manager.get_thread(thread_id).await {
-            self.submit_core_op(request_id, thread.as_ref(), Op::SetThreadName { name })
-                .await
-                .map_err(|err| internal_error(format!("failed to set thread name: {err}")))?;
-            return Ok((ThreadSetNameResponse {}, None));
-        }
-
         self.thread_store
             .update_thread_metadata(StoreUpdateThreadMetadataParams {
                 thread_id,