⚡ Bolt: Replace blocking time.sleep with asyncio.sleep in frame image endpoint

[benpiper]

💡 What: Replaced time.sleep(1) with await asyncio.sleep(1) in the /api/project/frame_image endpoint.
🎯 Why: Using time.sleep inside an async def function blocks the FastAPI event loop, causing the entire backend server to freeze and reject concurrent requests while waiting for a frame to extract.
📊 Impact: Prevents complete server stalls. Allows the backend to process hundreds of concurrent requests even while waiting for frames, reducing latency and avoiding timeout errors.
🔬 Measurement: Run a load test hitting /api/project/frame_image for an unextracted frame alongside a fast endpoint like /api/auth/status. The fast endpoint should return instantly instead of waiting up to 30 seconds.

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PR created automatically by Jules for task 14251507603111016048 started by @benpiper

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