[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/rollout/src/policy.rs

@@ -98,7 +98,6 @@ fn event_msg_persistence_mode(ev: &EventMsg) -> Option<EventPersistenceMode> {
         | EventMsg::AgentReasoningRawContent(_)
         | EventMsg::PatchApplyEnd(_)
         | EventMsg::TokenCount(_)
-        | EventMsg::ThreadNameUpdated(_)
         | EventMsg::ContextCompacted(_)
         | EventMsg::EnteredReviewMode(_)
         | EventMsg::ExitedReviewMode(_)