Meshtastic node Backup/Restore Implementation

TL;DR

Prevents node settings reset on power failure/device instabilities

Overview

This implementation adds a robust backup/restore system for Meshtastic node settings:

• Auto backup with rotation (survives interrupted writes)
• Golden backup (user-controlled snapshot of known-good state)
• Auto backup on shutdown
• InkHUD menu UI for manual backup/restore
• Admin message support for remote backup commands

Implementation Guide:

• Read BACKUP_IMPLEMENTATION.md

HowTo:

• Read BACKUP_USAGE.md

Merge branch

https://github.com/kuroanji/firmware/tree/auto_backup