Add BLE serial rig control and separate Bluetooth audio/control selection

[hedge31]

…tion

Contributed by BG7RHK, 2026-09.

Bluetooth rig control now supports BLE GATT UART (FFE0/FFE1 and Nordic NUS 6E400001/0002/0003) in addition to classic RFCOMM SPP.

Fixes:

• the device list only showed bonded devices, so unpaired BLE modules never appeared; it now also scans nearby BLE devices
• PTT writes failed because WRITE_NO_RESPONSE characteristics were rejected, and Nordic NUS used the notify characteristic for writes instead of 6E400002
• concurrent CAT writes at transmit time are now serialized through a queue

UI:

• the config screen gains a Bluetooth role selector (control/audio) so rig control devices and audio headsets are chosen separately

README: acknowledgement list updated with BG7RHK.