[feature] Sync Virtual Console button colour to RGB button custom feedback

[yestalgia]

Background

QLC+ allows users to assign MIDI feedback to buttons, including RGB colours for supported controllers like the Akai APC Mini MK2.

Currently, when a user assigns a colour to a Virtual Console button and also uses a custom feedback value, they must set the colour twice:

1. Set the Virtual Console button's appearance
2. Set the MIDI controller's button colour using the Custom Feedback dialogue

This is repetitive and unintuitive, users expect the colours to automatically match, especially when using RGB-capable controllers.

Goal

When a user assigns an input to a virtual console button, the default behaviour is changed when the input profile allows colours to be selected. Now, when the VC button colour is changed - the midi controller reflects this. If no colour is set for the button, Red for off, Green for on and Yellow for monitoring should be set.

Acceptance criteria

When a user assigns an input channel to a virtual console button, QLC+ will detect if a feedback-capable RGB MIDI controller is used. If so:

1. Add a small checkbox in the Button Properties UI: “Sync with VC Button Colour” (default: enabled)
2. Custom Feedback should automatically populate the On and Monitoring colour value with the closest match. The "off" value should be a slightly darker shade of the same colour.
3. When a button on the Virtual Console's colour has changed, the custom feedback should sync
4. The user should be able to override any or all of the colours chosen
   This feature should only apply to MIDI profiles that declare colour support.

Backward compatibility must be preserved for existing profiles and setups.