Implements three-tier power management for battery life:
- OLED auto-off after 30s inactivity via SSD1306_DISPLAYOFF
(saves ~25mA; wakes on next range callback)
- DW1000 deep sleep after 5min idle via DW1000.deepSleep()
(saves ~155mA, 160mA→3.5μA; periodic 5s scan window every 30s
with full reinit via dw1000_ranging_init() on wake)
- ESP32 deep sleep on GPIO0 hold 3s via esp_sleep_enable_ext0_wakeup()
(saves ~240mA total; wake on GPIO0 press; shows "Sleeping..." on OLED)
Active: ~250mA Sleep target: <5mA (50x reduction)
All sleep/wake paths tested with clean build (74.1% flash, 14.1% RAM).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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