fix(adminui): S7 typed page no longer wipes Tags on save

- S7DriverPage.FormModel now preserves Tags through Form ↔ Options
  translation (was hard-coding Tags = [] on every save, silently
  destroying any tag list that operators had configured).
- Add FormModel_RoundTrip tests for OpcUaClient and Historian
  mirror classes — both were translating Options ↔ form-model
  entirely untested.
- Surface S7 Tags in the round-trip test so this regression
  can't reach merge again.

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Clusters/Drivers/S7DriverPage.razor

@@ -300,6 +300,9 @@ else
         // Tags JSON view (read-only)
         public string? TagsJson { get; set; }
 
+        // Preserved originals (round-tripped unchanged from original options)
+        private IReadOnlyList<S7TagDefinition> _tags = [];
+
         // Common
         public string? ResilienceConfig { get; set; }
         public byte[] RowVersion { get; set; } = [];
@@ -326,6 +329,7 @@ else
                 ProbeTimeoutSeconds = (int)o.Probe.Timeout.TotalSeconds,
                 AdminProbeTimeoutSeconds = o.ProbeTimeoutSeconds,
                 TagsJson = tagsJson,
+                _tags = o.Tags,
             };
         }
 
@@ -344,8 +348,7 @@ else
                 Timeout = TimeSpan.FromSeconds(ProbeTimeoutSeconds),
             },
             ProbeTimeoutSeconds = AdminProbeTimeoutSeconds,
-            // Tags preserved from original JSON; this form does not edit the tag list.
-            Tags = [],
+            Tags = _tags,
         };
     }
 }