Auto: abcip-4.3 — diagnostic / system tags as browseable variables

Closes #240

docs/Driver.AbCip.Cli.md

@@ -56,6 +56,21 @@ otopcua-abcip-cli read -g ab://10.0.0.5/1,0 -t "Recipe[3]" --type Real
 otopcua-abcip-cli read -g ab://10.0.0.5/1,0 -t "Motor01.Speed" --type Real
 ```
 
+#### Diagnostic / system tags
+
+PR abcip-4.3 exposes five read-only diagnostic variables per device under
+`AbCip/<device>/_System/` in the OPC UA address space (see
+[AbCip-Operability §System tags](drivers/AbCip-Operability.md#system-tags--_system-folder)
+for the full table). These are not reachable through the AB CIP CLI — they
+live on the OPC UA server side, not the libplctag wire — so to read one,
+point the **OPC UA client** CLI at the running OtOpcUa server:
+
+```powershell
+# Read _ConnectionStatus for one device through the OPC UA server
+otopcua-client-cli read -u opc.tcp://localhost:4840 \
+    -n "ns=2;s=AbCip/ab://10.0.0.5/1,0/_System/_ConnectionStatus"
+```
+
 ### `write` — single Logix tag
 
 Same shape as `read` plus `-v`. Values parse per `--type` using invariant