feat(app-server): include turns page on thread resume (#23534)

## Summary

The client currently calls `thread/resume` to establish live updates and
immediately follows it with `thread/turns/list` to hydrate recent turns.
This lets `thread/resume` return that page directly, eliminating a round
trip and the ordering/deduplication gap between the two calls.

Experimental clients opt in with `initialTurnsPage: { limit,
sortDirection, itemsView }`. The response returns `initialTurnsPage` as
a `TurnsPage`, including cursors for paging further back in history.
Keeping the controls in a nested opt-in object provides the useful
`thread/turns/list` knobs without spreading page-specific parameters
across `thread/resume`.

## Verification

- `just fmt`
- `just write-app-server-schema --experimental`
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server
thread_resume_initial_turns_page_matches_requested_turns_list_page
--tests`
- `cargo test -p codex-app-server
thread_resume_rejoins_running_thread_even_with_override_mismatch
--tests`
- `just fix -p codex-app-server-protocol -p codex-app-server`

codex-rs/app-server/src/thread_state.rs

@@ -35,6 +35,8 @@ pub(crate) struct PendingThreadResumeRequest {
     pub(crate) emit_thread_goal_update: bool,
     pub(crate) thread_goal_state_db: Option<StateDbHandle>,
     pub(crate) include_turns: bool,
+    pub(crate) initial_turns_page:
+        Option<codex_app_server_protocol::ThreadResumeInitialTurnsPageParams>,
     pub(crate) redact_resume_payloads: bool,
 }