AMOLED brightness fades to 0 after IDLE_TIMEOUT_MS without a physical
button press; any of the three buttons (BTN_BACK / BTN_FWD / PWR) fades
it back in. The first press from sleep is consumed for wake only —
Space / Shift+Tab / cycle-screen only fire on the second press, so
reaching for the device to glance at it doesn't accidentally send PTT
to Claude.
Touch never counts as activity and is fully swallowed while asleep:
pets and sleeves can't wake it, and LVGL can't secretly toggle
splash<->usage behind a black panel.
Rotation handling defers while asleep so its blank+ramp doesn't fight
the idle fade; a rotation that happens during sleep is detected and
ramped in on wake.
All tunables live in idle_cfg.h (timeout, fade durations, default
brightness) — nothing is hard-coded in main.cpp.
AMOLED brightness=0 is true 0 emission on these self-emissive panels,
so no extra power-management plumbing (light-sleep, AXP rail gating)
is needed to get the battery savings.
