Add Battery Percentage Display Feature

[yug49]

 Added a new feature that allows users to toggle the display of battery percentage in the status bar.

Details

• Added battery percentage label to the status bar that shows quantized battery levels.
• Added toggle switch in Display Settings to enable/disable battery percentage visibility
• Battery percentage setting is persisted across app restarts
• Quantized Display: Battery percentage is shown in 20% increments with hysteresis to prevent flickering:

  Actual %	Discharging	Charging
  0-20%	20%	0%
  21-40%	40%	20%
  41-60%	60%	40%
  61-80%	80%	60%
  81-100%	100%	80%
  95%+ (charging)	-	100%

Before

After

With USB icon

Related Issue

Closes #1976