Remove the "clock cannot go backwards" restriction from all set-time
paths (CLI `time`, `clock sync`, companion radio CMD_SET_DEVICE_TIME,
and simple_secure_chat). The ESP32-S3 RTC drifts 5-10% during deep
sleep, making backwards correction necessary after even a few days.
Add safeElapsedSecs() helper in ArduinoHelpers.h that clamps elapsed
time to 0 when a stored timestamp appears to be in the future after a
clock correction. Applied to:
- Neighbor "heard X ago" displays in simple_repeater
- UI time displays in companion_radio
- TimeSeriesData calculations in simple_sensor
Switch BaseChatMesh connection expiry from RTC timestamps to monotonic
millis(), making it immune to RTC adjustments from GPS, NTP, or manual
sync. Rename last_activity to last_activity_ms to reflect the change.
