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

docs/drivers/OpcUaClient.md

@@ -38,8 +38,7 @@ out-of-process isolation.
       "EndpointUrl": "opc.tcp://plc.internal:4840",
       "SecurityPolicy": "None",
       "SecurityMode": "None",
-      "AuthType": "Anonymous",
-      "TargetNamespaceKind": "Equipment"
+      "AuthType": "Anonymous"
     }
   }
 }
@@ -62,19 +61,21 @@ dangle. Stored NodeIds embed the server-stable namespace **URI** (not the
 session-relative `ns=N` index) so a remote namespace-table reorder across a
 restart doesn't silently re-point references at the wrong namespace.
 
-### Namespace assignment
+### Namespace assignment (retired, Gitea #648)
 
-This is the only driver that gateways into **either** namespace kind, decided
-per instance via `TargetNamespaceKind`:
+Earlier versions required a per-instance `TargetNamespaceKind` (`Equipment` +
+a mandatory `UnsMappingTable`, or `SystemPlatform` + an empty table). Both
+options are **removed**: nothing ever read the mapping table beyond the startup
+check, and in v3 the raw-to-UNS projection is explicit (`UnsTagReference`), so
+the choice carried no behaviour — it only made a config without the key fail
+`Initialize`. Remote nodes are authored as `/raw` tags bound by their upstream
+`nodeId`; there is no namespace field on the driver, the AdminUI form or the
+seed.
 
-- `Equipment` — the remote server exposes raw equipment data; remote browse
-  paths are remapped to UNS via a required `UnsMappingTable`.
-- `SystemPlatform` — the remote server exposes processed/derived data; the
-  remote hierarchy is preserved with no UNS conversion (and the mapping table
-  must be empty).
-
-The choice is enforced at startup so a misconfiguration fails draft validation
-rather than surfacing as a runtime surprise.
+Stored `DriverConfig` JSON that still carries `targetNamespaceKind` or
+`unsMappingTable` keeps working: the keys are unknown and ignored on parse and
+initialise (the AdminUI form drops them on the next save). Pinned by
+`OpcUaClientReinitConfigAdoptionTests.Legacy_namespace_keys_are_ignored_by_parse_and_initialise`.
 
 ## Capability surface