Companion power and system-watchdog diagnostics

Companion text commands are available through its existing USB terminal and framed CLI paths, with the same admission rules as other diagnostics:

power
get pwrmgt.support
get pwrmgt.source
get pwrmgt.bootmv
get system.watchdog

power reports the current battery millivolts, USB power, solar charging, external power and charger state. A board without a dedicated USB or solar detector reports n/a for that field. External or charging power does not prove that USB data is connected.

get pwrmgt.support reports whether the board includes nRF52 power management. On supported builds, get pwrmgt.source reports external or battery, and get pwrmgt.bootmv reports the boot-time voltage sample. The boot sample differs from the live battery reading. Other builds return an explicit unsupported reply for the source and boot-voltage queries.

On nRF52, get system.watchdog reports the hardware watchdog's actual running state as on or off. It does not start or feed the watchdog. This also works when a build disables normal watchdog feeding or inherits a running watchdog from its bootloader. Other platforms report unsupported; this command does not describe an ESP32 task watchdog or the radio-recovery watchdogs.

Companion normally starts and feeds its nRF52 watchdog in the application loop. Its timeout is normally 60 seconds. Companion has no saved watchdog enable preference, so set system.watchdog returns an explicit error. Infrastructure roles retain their existing saved on/off policy. Implementing that control in Companion would also require preference storage and feed-loop integration: an already running nRF52 watchdog cannot be stopped directly.