fix(dcl+centralui): MxGateway tag browse — lazy attributes, frame-size cap, wider scrollable picker

Expanding a Galaxy object in the tag picker hung on "loading…": the browse
reply inlined every child's full attribute set (~152 KB), exceeding Akka's
128 KB remote frame, and remoting silently discarded the oversized reply.

Browse path (DataConnectionLayer):
- RealMxGatewayClient: navigation now uses BrowseChildren(include_attributes=
  false) — child objects only — and an object's own attributes load lazily via
  DiscoverHierarchy(root, max_depth=0) when it's expanded. Payload drops from
  ~152 KB/level to a few KB. Seam contract unchanged.
- DataConnectionActor.CapBrowseChildren: protocol-agnostic byte-budget cap
  (~100 KB) on every BrowseNodeResult before it crosses the site→central
  frame, OR-ing the adapter's own Truncated flag. Byte budget, not a count —
  the only bound that holds regardless of NodeId/attribute-name length.
- RealOpcUaClient: requestedMaxReferencesPerNode 1000 → 500 to narrow the
  window before the byte budget applies.
- Graceful gRPC Unimplemented handling → NotSupportedException →
  BrowseFailureKind.NotBrowsable with an actionable message (older gateway
  builds lacking BrowseChildren).

Picker UI (CentralUI):
- NodeBrowserDialog: modal-lg → modal-xl; new scoped .razor.css caps the tree
  at 55vh with its own scrollbar so manual entry + Select/Cancel stay visible.
- Protocol-agnostic failure messages (was hardcoded "OPC UA …"); renamed the
  leftover opcua-browser-tree class to node-browser-tree.

Tests: new frame-budget cap test + NotSupported=>NotBrowsable mapping test;
DCL suite 88/88. Doc: Component-DataConnectionLayer.md records the lazy
attribute-light browse and the frame-size guard.

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Dialogs/NodeBrowserDialog.razor

@@ -6,7 +6,7 @@
 @if (_isVisible)
 {
     <div class="modal show d-block" tabindex="-1" role="dialog" style="background-color: rgba(0,0,0,0.5);">
-        <div class="modal-dialog modal-lg" role="document">
+        <div class="modal-dialog modal-xl" role="document">
             <div class="modal-content">
                 <div class="modal-header">
                     <h5 class="modal-title">Browse — @ConnectionName</h5>
@@ -21,7 +21,7 @@
                         </div>
                     }
 
-                    <div class="opcua-browser-tree">
+                    <div class="node-browser-tree">
                         @if (_rootNodes.Count == 0 && _failure is null)
                         {
                             <em class="text-muted">Loading…</em>
@@ -167,20 +167,25 @@
         _manualNodeId = node.NodeId;
     }
 
-    // Task 17: map each BrowseFailureKind to a friendly UI message. The raw
-    // failure.Message is surfaced verbatim only for ServerError (which carries
-    // the OPC UA SDK's own Bad_* text) and as the default fallback for any
-    // future failure kind added without a UI mapping.
+    // Task 17: map each BrowseFailureKind to a friendly UI message. Messages are
+    // protocol-agnostic (the dialog serves every browsable protocol — OPC UA,
+    // MxGateway, …). The raw failure.Message is surfaced verbatim for ServerError
+    // (which carries the underlying protocol SDK's own error text), for
+    // NotBrowsable when the adapter supplied a reason (e.g. a gateway build that
+    // lacks the browse RPC), and as the default fallback for any future failure
+    // kind added without a UI mapping.
     private void SetFailure(BrowseFailure failure)
     {
         _failure = failure;
         _failureMessage = failure.Kind switch
         {
             BrowseFailureKind.ConnectionNotFound      => "Connection no longer exists at the site.",
-            BrowseFailureKind.ConnectionNotConnected  => "OPC UA session not connected — retry shortly or use manual entry.",
-            BrowseFailureKind.NotBrowsable            => "This connection does not support browsing.",
+            BrowseFailureKind.ConnectionNotConnected  => "Connection not connected — retry shortly or use manual entry.",
+            BrowseFailureKind.NotBrowsable            => string.IsNullOrWhiteSpace(failure.Message)
+                                                            ? "This connection does not support browsing."
+                                                            : failure.Message,
             BrowseFailureKind.Timeout                 => "Browse timed out — the server may be slow. Try again or enter the node id manually.",
-            BrowseFailureKind.ServerError             => $"OPC UA server error: {failure.Message}",
+            BrowseFailureKind.ServerError             => $"Server error: {failure.Message}",
             _                                          => failure.Message
         };
         StateHasChanged();

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Dialogs/NodeBrowserDialog.razor.css

@@ -0,0 +1,14 @@
+/* Scoped styles for the protocol-agnostic tag browse dialog. */
+
+/* Cap the tree's height and let it scroll independently so deep hierarchies
+   (e.g. a Galaxy with many objects/attributes) don't push the manual-entry
+   field and Select/Cancel buttons off-screen. Both axes scroll: vertical for
+   long sibling lists, horizontal for deeply-indented nested nodes. */
+.node-browser-tree {
+    max-height: 55vh;
+    overflow: auto;
+    border: 1px solid var(--bs-border-color, #dee2e6);
+    border-radius: 0.375rem;
+    padding: 0.5rem 0.75rem;
+    background-color: var(--bs-body-bg, #fff);
+}