Repeater mode: device auto-relays MeshCore packets when no app is
connected. Enabled by default, toggle with AT+REPEATER=0/1. Includes
deduplication ring and random jitter to prevent loops.
Prebuilt binary: added CI workflow that builds a merged .bin on tag
push so users can flash without installing the Xtensa toolchain.
Protocol hot-switching: auto-resets to detection mode on serial
inactivity (30s) or BLE disconnect. AT+SWITCH for manual reset.
Also: gated test beacons when app connected, updated README with
flash instructions and AT command reference.
