Extends the battery header setting from a %/V toggle into a 3-state
option (Percentage / Voltage / Bars), encoded across two option bits so
existing codeplugs keep reading as Percentage.
Bars renders a battery-shaped icon (outlined body + terminal nub) with
up to 4 segments, each representing 25% of charge, and blinks the fill
when the battery is low.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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