Add an optional "Screen Dim" setting (Display Options) that, in Auto backlight
mode, dims the screen to a fraction of the configured brightness after the
backlight timeout instead of going to the off level. Any activity restores full
brightness.
- Setting values: Off / 100% / 50% / 30%, stored in two spare option bits
(no settingsStruct change, no version bump; existing codeplugs default to Off).
- display.c: displayGetIdleBacklightPercentage() computes the idle level.
- applicationMain.c: the idle-timeout tick dims to that level; an incoming
signal (hasSignal) re-triggers full brightness so RX keeps the screen lit.
TX already forces full brightness.
- menuDisplayOptions.c: new entry with a hardcoded English label (no language
files touched).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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