Remove camera features and auto-start worker services

[mkalter]

Summary

• remove camera streaming configuration, endpoints, and stream directory handling from the FastAPI backend
• add a ServiceProcessManager that launches printer_uploader.py, slicer.py, and queue_service.py on startup and shuts them down cleanly on shutdown

Testing

• python -m compileall server.py printer_uploader.py queue_service.py slicer.py

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https://chatgpt.com/codex/tasks/task_b_68ecb15f38608325a3ae52313f74019d