Attach packet drivers to initially empty ETCP connections. Share BLE neighbor
tracking and group fallback between desktop and Android in cgathui_common.
Deliver join links through a dedicated Write/Indicate characteristic with
independent fragmentation queues, application acknowledgements, deduplication
and bounded retries. Merge LAN/BLE discovery and add a separate Bluetooth
invitation reception setting to both clients.
Validation: 230 core tests, BLE transport/BlueZ/UI tests, ASAN/UBSAN,
Linux GUI and Android builds, and Windows backend cross-compilation.
Physical Android/Linux invitation exchange passed with either GATT initiator.
The Android-initiated run also verified all 32 ETCP packets of 1500 bytes;
the desktop-initiated load run reached 7/32 within its 45-second time limit.
evgeny