feat: enhance chat history loading with new hooks and UI components (#2338)

* Refactor API fetch calls to use a unified fetch function; enhance chat history loading with new hooks and UI components

- Replaced `fetchWithAuth` with a generic `fetch` function across various API modules for consistency.
- Updated `useThreadStream` and `useThreadHistory` hooks to manage chat history loading, including loading states and pagination.
- Introduced `LoadMoreHistoryIndicator` component for better user experience when loading more chat history.
- Enhanced message handling in `MessageList` to accommodate new loading states and history management.
- Added support for run messages in the thread context, improving the overall message handling logic.
- Updated translations for loading indicators in English and Chinese.

* Fix test assertions for run ordering in RunManager tests

- Updated assertions in `test_list_by_thread` to reflect correct ordering of runs.
- Modified `test_list_by_thread_is_stable_when_timestamps_tie` to ensure stable ordering when timestamps are tied.

backend/app/gateway/services.py

@@ -213,21 +213,6 @@ async def start_run(
 
     disconnect = DisconnectMode.cancel if body.on_disconnect == "cancel" else DisconnectMode.continue_
 
-    # Resolve follow_up_to_run_id: explicit from request, or auto-detect from latest successful run
-    follow_up_to_run_id = getattr(body, "follow_up_to_run_id", None)
-    if follow_up_to_run_id is None:
-        run_store = get_run_store(request)
-        try:
-            recent_runs = await run_store.list_by_thread(thread_id, limit=1)
-            if recent_runs and recent_runs[0].get("status") == "success":
-                follow_up_to_run_id = recent_runs[0]["run_id"]
-        except Exception:
-            pass  # Don't block run creation
-
-    # Enrich base context with per-run field
-    if follow_up_to_run_id:
-        run_ctx = dataclasses.replace(run_ctx, follow_up_to_run_id=follow_up_to_run_id)
-
     try:
         record = await run_mgr.create_or_reject(
             thread_id,
@@ -236,7 +221,6 @@ async def start_run(
             metadata=body.metadata or {},
             kwargs={"input": body.input, "config": body.config},
             multitask_strategy=body.multitask_strategy,
-            follow_up_to_run_id=follow_up_to_run_id,
         )
     except ConflictError as exc:
         raise HTTPException(status_code=409, detail=str(exc)) from exc