Replace custom async_helpers.py with FastAPI BackgroundTasks / anyio

Problem

app/utils/async_helpers.py (~153 LOC) implements a custom bridge for running async coroutines from sync contexts — including manual event loop detection, daemon thread spawning, and custom error handlers. This pattern is fragile and a common source of hard-to-reproduce bugs (e.g. RuntimeError: This event loop is already running).

The primary use case is broadcasting SocketIO queue updates after synchronous service calls.

Affected Files

• app/utils/async_helpers.py
• app/services/consultation_queue_service.py (calls run_async_task())

Fix

• Use FastAPI's built-in BackgroundTasks to dispatch the SocketIO broadcast after a response
• Or adopt anyio.from_thread.run_sync() / anyio.to_thread.run_sync() which is already a transitive dependency via FastAPI

References

• https://anyio.readthedocs.io/en/stable/threads.html
• FastAPI BackgroundTasks: https://fastapi.tiangolo.com/tutorial/background-tasks/

Effort

Medium (~2h)