Finish firmware private transport stack

docs/host_dri_rebuild.md

@@ -62,7 +62,30 @@ Implemented behavior:
 - collect device name and address
 - filter to `LowEnergyCoreConfiguration`
 - stop after a short timeout
-### Node 3: CDC transport cleanup
+
+### Node 3: GATT open and raw byte transport
+
+Files updated in this step:
+
+- `KeyBorad/KeyBorad/DRI/GATT/Dri_Gatt.h`
+- `KeyBorad/KeyBorad/DRI/GATT/Dri_Gatt.cpp`
+
+Design notes:
+
+- keep transport-only responsibility
+- use Qt Bluetooth instead of custom Win32 BLE code
+- connect, discover service, subscribe, then pass raw bytes upward
+
+Implemented behavior:
+
+- connect to a BLE device by address
+- discover the target custom service
+- resolve RX/TX characteristics
+- enable notify on TX
+- queue raw bytes from TX notify
+- write raw bytes to RX characteristic
+
+### Node 4: CDC transport cleanup
 
 Files updated in this step: