Support legacy views for paginated thread history (#34085)

## Why

Clients that use full-history resume or request full items in turn pages should
work consistently across legacy and paginated threads.

## What changed

- Materialize complete turns and items from the paginated projection for
  `thread/resume` and `thread/turns/list` when requested.
- Support `initialTurnsPage` during paginated resume, including merging a live
  active turn while preserving the requested page size and cursors.
- Keep metadata-only resume behavior and backwards cursors available through
  `excludeTurns: true`.

## Testing

- Extend app-server coverage for full paginated history, full item views, and
  initial resume pages on running threads.

GitOrigin-RevId: e340f44d631ce135895c95d7e1baa7bfecd86e71

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

@@ -40,6 +40,10 @@ pub(crate) struct PendingThreadResumeRequest {
     pub(crate) include_turns: bool,
     pub(crate) initial_turns_page:
         Option<codex_app_server_protocol::ThreadResumeInitialTurnsPageParams>,
+    pub(crate) paginated_turns: Option<Vec<Turn>>,
+    pub(crate) paginated_initial_turns_page: Option<codex_app_server_protocol::TurnsPage>,
+    pub(crate) paginated_initial_turns_page_with_active_slot:
+        Option<codex_app_server_protocol::TurnsPage>,
     pub(crate) resume_cursor_store: Option<Arc<dyn codex_thread_store::ThreadStore>>,
     pub(crate) redact_resume_payloads: bool,
 }