Document RuntimeState concurrency model and mark task 5 complete

backend/app/utils/runtime_state.py

@@ -5,6 +5,12 @@ exposed through a controlled state manager object. This keeps the FastAPI
 framework state bag limited to shared infrastructure handles and immutable
 configuration while still allowing existing code to access runtime values via
 attribute proxying.
+
+RuntimeState is designed for a single-process, single-worker asyncio
+deployment. Mutations must complete without awaiting across read-modify-write
+sequences. If BanGUI is ever deployed with multiple workers or across processes,
+this module must be replaced with a shared backend such as Redis or shared
+memory.
 """
 
 from __future__ import annotations
@@ -13,9 +19,8 @@ import datetime
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any
 
-from starlette.datastructures import State
-
 import structlog
+from starlette.datastructures import State
 
 from app.models.config import PendingRecovery
 from app.models.server import ServerStatus