Add Reticulum destination hash indicator at the top of the captive-portal
config page so users can identify the device.
- Store the 32-char hex destination hash in RTC_NOINIT memory after RNS
starts on a normal boot (survives software reboots into config mode)
- BoundaryConfig.h reads the RTC value and renders a styled hash box at
the top of the HTML page, above the config form
- Falls back to a friendly placeholder if the device has never completed
a normal boot (hash not yet assigned)
- Rebuild precompiled firmware for Heltec V3 and V4 boundary variants
