[MIDI] Implement MIDI Input/Output ComboBoxes in HeaderPanel

[tensquaresoftware]

Add MIDI device selection ComboBoxes in the HeaderPanel to allow users to choose MIDI input and output devices.

Tasks:

• Create MIDI Input ComboBox widget in HeaderPanel
• Create MIDI Output ComboBox widget in HeaderPanel
• Populate ComboBoxes with available MIDI devices from system
• Wire selection to MidiManager for device connection
• Test MIDI communication with Matrix-1000 hardware

Context:
Users need to select which MIDI devices to use for communication with the Matrix-1000 synthesizer.