fix(modbus): review r2 - region+address keys always win; string-only means no keys

N2: pre-#741 rows carry region/address beside an addressString with no marker
(the old driver never read the string, the old model preserved it as an
unknown key). The r1 rule resolved those from the string - a silent remap or
BadNodeIdUnknown on upgrade. The driver now loads from region+address whenever
both are present (classic, editor-pinned, pre-lane); only a blob with NO keys
is string-only and resolved through the parser. This is safe because the model
no longer stamps keys onto a string-only tag. The model distinguishes
string-only / legacy-string-beside-keys / pinned, and the editor hint says so.
Test matrix over every persisted shape (keys only, pre-lane keys+string,
pre-lane stamped HR/0+string, string only, marker+keys, marker no keys) under
every family; the pre-lane row also through a model save and a CSV
export->import.
n5: a typed CSV address cell is an authored address - it drops addressString
and the marker (new CsvTypedColumn.ClearsKeys) instead of being discarded.
n6: Validate skips the region/dataType/byteOrder enum checks on a string-only
tag (the driver ignores them). n7: docs/v2/modbus-addressing.md restates the
key-presence rule.

Refs #741
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/ModbusTagConfigEditor.razor

@@ -18,6 +18,10 @@
     {
         <div class="col-12"><div class="form-text text-warning">String-only tag: the driver resolves <code>@_m.AddressString</code> with its own family (here @_family). The fields below are NOT its address — press Resolve to pin them, or edit a field to replace the string.</div></div>
     }
+    else if (_m.HasLegacyAddressString)
+    {
+        <div class="col-12"><div class="form-text">This tag carries a legacy address string <code>@_m.AddressString</code> that the driver does not use: the fields below are its address. Press Resolve to re-pin it from the string with the driver family.</div></div>
+    }
     else if (_m.AddressString is not null)
     {
         <div class="col-12"><div class="form-text">Resolved from <code>@_m.AddressString</code> (family @_family) and pinned: the fields below are what the driver polls, so a later family change does not remap the tag. Editing a field drops the string.</div></div>