Add printer connection state reporting and update sender UI

[peterwolf-pl]

Summary

• broadcast machine state (READY/BUSY/ERROR) over serial and TCP, clearing stale buffers when clients reconnect
• lower the starting step rate for smoother accel/decel and align sender defaults with firmware values
• improve the Python sender to display Wi-Fi connection status, show state updates, and surface disconnect/errors cleanly
• update the Flask UI sender to show live Wi-Fi link state and machine status, match motion defaults with the firmware, and paste full ACODE into the Printer tab when pushing from any generator

Testing

• python -m compileall print.py
• python -m compileall ui_sender.py

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