refactor(opcuaclient): remove vestigial TargetNamespaceKind + UnsMappingTable (#648)

Nothing read the mapping table beyond the startup validator; v3 UNS projection is
explicit via UnsTagReference. Legacy keys in stored DriverConfig are ignored (pinned).
Reverts the docker-dev opc-plc seed workaround from fdee129f.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docker-dev/seed/seed-clusters.sql

@@ -218,7 +218,7 @@ DECLARE @OpcPlcAlarmSourceNodeId nvarchar(400) = N'';   -- e.g. N'ns=3;s=<source
 IF NOT EXISTS (SELECT 1 FROM dbo.DriverInstance WHERE DriverInstanceId = 'MAIN-opcua')
   INSERT dbo.DriverInstance(DriverInstanceId, ClusterId, RawFolderId, Name, DriverType, DriverConfig, Enabled)
   VALUES ('MAIN-opcua', 'MAIN', NULL, 'opcplc', 'OpcUaClient',
-          N'{ "SecurityPolicy": "None", "SecurityMode": "None", "AuthType": "Anonymous", "AutoAcceptCertificates": true, "TargetNamespaceKind": "SystemPlatform" }', 1);
+          N'{ "SecurityPolicy": "None", "SecurityMode": "None", "AuthType": "Anonymous", "AutoAcceptCertificates": true }', 1);
 IF NOT EXISTS (SELECT 1 FROM dbo.Device WHERE DeviceId = 'MAIN-opcua-dev')
   INSERT dbo.Device(DeviceId, DriverInstanceId, Name, Enabled, DeviceConfig)
   VALUES ('MAIN-opcua-dev', 'MAIN-opcua', 'plc', 1, N'{ "EndpointUrl": "opc.tcp://10.100.0.35:50000" }');