⚡ Bolt: Prevent event loop blocking in frame image fetch

[benpiper]

💡 What

Replaced a synchronous time.sleep(1) with await asyncio.sleep(1) inside the get_frame_image asynchronous route handler in backend/main.py. Also removed an unused import time statement to clean up imports.

🎯 Why

In FastAPI, async def endpoints execute on the single main event loop thread. Calling a synchronous blocking function like time.sleep() halts the thread entirely, preventing the server from processing any other requests concurrently while waiting for the frame file to be generated. Using await asyncio.sleep() correctly yields execution back to the event loop, ensuring the application remains highly responsive and performant.

📊 Impact

Eliminates a massive concurrency bottleneck. Previously, fetching a frame image that took 30 seconds to generate would lock up the server completely for 30 seconds. Now, the server can handle unlimited concurrent requests while waiting for the file to be created.

🔬 Measurement

1. Start the server and initiate an extraction or action that triggers get_frame_image.
2. Simultaneously send multiple requests to other endpoints (like /api/auth/me).
3. Observe that the other endpoints return immediately rather than hanging until the frame image is served.

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PR created automatically by Jules for task 707313536607418233 started by @benpiper

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