Wake up periodically to refresh the battery display

At the moment, you could go to sleep and never wake up as the battery would have died.

We should probably wake up every hour or so to refresh the battery display - maybe could get fancy and show a needs charging icon if the battery is very low.

Start by locating the battery display code and the sleep/wake entry points in the ESP32 application. Trace how battery state is currently refreshed, then determine the existing wake mechanism and define done as periodically refreshing the display after wake, with the low-battery icon treated as an optional separate outcome.

Written by the indexing model from the issue text.