Added Backlight toggle on new quad-click button event

[saradonim]

This aligns companion radio firmware with the stock LilyGo T-Echo behavior, which also uses quad-click to toggle the backlight.

Highlights

• Added BUTTON_EVENT_QUAD_CLICK to MomentaryButton for detecting 4 consecutive clicks
• Quad-clicking the user button toggles a "forced backlight" mode, keeping the backlight always on
• Added showAlert() feedback to both toggleBuzzer() and toggleBacklight() to notify the user when the requested hardware is not available. This reduces confusion when triple/quad clicks appear to do nothing.