The previous commit fixed battery_mv in the STATS_TYPE_CORE frame, but that is
not the path companion apps use to display battery. CMD_GET_BATT_AND_STORAGE
goes through `CompanionFrameServer._get_batt_and_storage()`, an openhop_core
extension hook documented as "Default: all zeros" that the repeater never
overrode — so apps showed 0% regardless of what any sensor reported.
Override it in the repeater's frame server: battery from the same sensor lookup
added for core stats, storage from the filesystem holding the configured
storage_dir. Both are wired in from main.py alongside stats_getter.
Found by deploying the previous fix and observing that Home Assistant showed the
modem battery correctly while the phone app still showed 0% — two different
paths, only one of which had been fixed.
`_get_companion_stats` hardcoded `battery_mv: 0`, so every MeshCore companion
client connected to a Python repeater showed no battery, even when a sensor
plug-in was reporting one. The protocol side is already complete: the frame
server packs `battery_mv` into the STATS_TYPE_CORE frame and clients request it
via CMD_GET_BATT_AND_STORAGE.
Surface the first sensor reading that publishes a usable battery voltage,
accepting either `battery_voltage_mv` or `battery_voltage_v`. This covers an
attached UPS HAT as well as the battery of an openHop modem the repeater is
driving, which is the case that prompted this: a solar-powered modem whose
battery was invisible to the companion app right up until it went flat.
Returns 0 when no sensor reports a battery, which is what clients already
expect from a mains-powered node, and the lookup never raises — stats must
not be able to take down the companion connection.
skjegg