review(AdminUI): fix null-TagConfig crash, CTS leak, unencoded historian tag

Review at HEAD 7286d320. AdminUI-002: IsValidJson null/blank -> friendly error (was
ArgumentNullException). AdminUI-003: DriverStatusPanel Reconnect/Restart dispose CTS (build-
verified, live /run deferred). AdminUI-005: HistorianWonderware picker URL-encodes tag name.
AdminUI-008: Format round-trip test. 001 (script-page authz) + 004 (hub [Authorize]) left
Open as cross-cutting w/ Host/Security.

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverStatusPanel.razor

@@ -227,9 +227,10 @@
         try
         {
             var userName = await GetCurrentUserNameAsync();
+            using var cts = new System.Threading.CancellationTokenSource(TimeSpan.FromSeconds(15));
             var result = await AdminOps.AskAsync<ReconnectDriverResult>(
                 new ReconnectDriver(ClusterId, DriverInstanceId, userName, Guid.NewGuid()),
-                new System.Threading.CancellationTokenSource(TimeSpan.FromSeconds(15)).Token);
+                cts.Token);
             ShowOpResult(result.Ok, result.Ok ? "Reconnect dispatched" : (result.Message ?? "Failed"));
         }
         catch (Exception ex)
@@ -252,9 +253,10 @@
         try
         {
             var userName = await GetCurrentUserNameAsync();
+            using var cts = new System.Threading.CancellationTokenSource(TimeSpan.FromSeconds(15));
             var result = await AdminOps.AskAsync<RestartDriverResult>(
                 new RestartDriver(ClusterId, DriverInstanceId, userName, Guid.NewGuid()),
-                new System.Threading.CancellationTokenSource(TimeSpan.FromSeconds(15)).Token);
+                cts.Token);
             ShowOpResult(result.Ok, result.Ok ? "Restart dispatched" : (result.Message ?? "Failed"));
         }
         catch (Exception ex)

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/Pickers/HistorianWonderwareAddressBuilder.cs

@@ -8,5 +8,8 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared.Drivers.Pickers;
 public static class HistorianWonderwareAddressBuilder
 {
     public static string Build(string tagName, string mode, int interval)
-        => $"{tagName}?mode={mode}&interval={interval}";
+        // Percent-encode the tag name so a name carrying query-reserved characters (? & # =) can't
+        // corrupt the produced query string (AdminUI-005). Mode is a fixed enum-style token, so it
+        // needs no encoding.
+        => $"{Uri.EscapeDataString(tagName)}?mode={mode}&interval={interval}";
 }

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs

@@ -1280,9 +1280,17 @@ public sealed class UnsTreeService(IDbContextFactory<OtOpcUaConfigDbContext> dbF
         return null;
     }
 
-    /// <summary>Returns <c>true</c> if <paramref name="json"/> parses as a well-formed JSON document.</summary>
-    private static bool IsValidJson(string json)
+    /// <summary>Returns <c>true</c> if <paramref name="json"/> parses as a well-formed JSON document.
+    /// Null/blank input is treated as invalid (not well-formed JSON) so every caller gets the friendly
+    /// "not valid JSON" result rather than an unhandled <see cref="ArgumentNullException"/> from
+    /// <c>JsonDocument.Parse(null)</c> (AdminUI-002).</summary>
+    private static bool IsValidJson(string? json)
     {
+        if (string.IsNullOrWhiteSpace(json))
+        {
+            return false;
+        }
+
         try
         {
             using var _ = System.Text.Json.JsonDocument.Parse(json);