fix(authoring): CSV import accepts variable-length arrays; Plain MQTT isArray warns at authoring (lmxopcua#770)

CSV: IsArray with blank/0 ArrayLength is the variable-length shape browse-commit and the composer produce, so its own export now re-imports.
Plain MQTT: MqttTagDefinitionFactory.Inspect (the driver's parse, consulted by the authoring inspector) now advises when isArray is set on a Plain-shaped tag; Sparkplug-shaped blobs stay quiet.
Live Sparkplug array test and SDK reflection items remain open.

Claude-Session: https://claude.ai/code/session_01GT67AEHd2Acv1YPwGfXEoV

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Contracts/MqttTagDefinitionFactory.cs

@@ -431,6 +431,22 @@ public static class MqttTagDefinitionFactory
                 + "never bind and will read BadNodeIdUnknown in Sparkplug B mode.");
         }
 
+        // isArray on a PLAIN-shaped tag (lmxopcua#770). The composer materialises the node from isArray
+        // (ValueRank=1) in every mode, but only the Sparkplug ingest path ever feeds it an array: a Plain
+        // tag decodes ONE scalar per message, so the node would be an array fed scalar values. Warned only
+        // when the Plain reader takes the blob and the Sparkplug one does not (a Sparkplug blob carrying a
+        // leftover topic key is a legitimate array tag and must stay quiet — a gate stricter than the runtime).
+        if (accepted && ReadArrayShape(root).IsArray
+            && FromTagConfig(root.GetRawText(), InspectionRawPath, out _)
+            && !FromSparkplugTagConfig(root.GetRawText(), InspectionRawPath, out _))
+        {
+            advisories.Add(
+                "'isArray' is set on a Plain-mode tag: Plain MQTT decodes one scalar per message and never "
+                + "produces an array, so the tag would be an array node fed scalar values. 'isArray' is "
+                + "honoured only in Sparkplug B mode (array metrics) — remove it, or switch the driver to "
+                + "Sparkplug B.");
+        }
+
         // The ONE key whose verdict depends on the DRIVER'S mode, reported as an
         // advisory because no tag-level gate can see that mode. A present-but-invalid payloadFormat is
         // fatal to the Plain parse and invisible to the Sparkplug one, so a union accept here can only