API: blocking sync work in async handlers freezes the event loop

[I4cTime]

Summary

Several handlers are async def but do long blocking I/O directly (not via threadpool), stalling every other in-flight request - including the auth-exempt /health probe Electron polls.

Locations

• src/game_setup_hub/api/routes/saves.py:25-51 - backup zips up to 4 GB / 50k files synchronously
• routes/utility.py:185-230 (prefix info / delete, shutil.rmtree)
• routes/games.py:33-44 (discover_games() filesystem scan)

Failure scenario

User triggers a save backup of a large prefix -> the whole API is unresponsive for the duration -> the UI hangs and concurrent requests (health poll, other panels) block until the zip finishes.

Fix

Make these def handlers (FastAPI runs them in the threadpool) or await run_in_threadpool(...).