Add commander-style Moonraker UI for ARA6D control

[Patvscode]

Motivation

• Provide a commander-like desktop UI that works with the ARA6D stack (Moonraker/Klipper + AS5600 encoders) instead of the PAROL6 control board.
• Keep a familiar operator UX (joint/cartesian jogging, macros, telemetry) while using G-code/Moonraker as the motion interface.
• Make encoder feedback usable by the UI via a serial reader for AS5600/ESP32 streams.

Description

• Replace the prototype desktop_app/main.py with a new CommanderApp implementation that includes MoonrakerClient, EncoderReader, and a Tk ttk UI for joint/cart jogs, macros, custom G-code send, and encoder display.
• Implement config load/save via desktop_app/config.json and use templated jog macros such as JOINT_JOG J={joint} D={delta} F={feedrate} and CART_JOG X={x} ... to translate UI actions into Moonraker G-code calls.
• Add a serial EncoderReader thread to parse simple text/JSON encoder lines and surface joint values in the UI, and add pyserial to desktop_app/requirements.txt.
• Provide helper methods MoonrakerClient.send_gcode and get_printer_info, plus UI controls for connecting, saving settings, and restarting encoder reading.

Testing

• No automated tests were executed for this change (GUI application); the patch was added and committed but no CI/unit tests were run.
• Basic runtime inspection (file presence and importable dependencies) was performed during development but no end-to-end execution against Moonraker or physical encoders was run.
• Manual verification of source layout and configuration file creation was performed by the change process (no pass/fail status to report).
• Recommend running the GUI (python3 desktop_app/main.py) and connecting to a test Moonraker instance and optional encoder serial stream for functional verification.

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Codex Task