fix(adminui,client): error boundary inside the interactive scope, stale-commit OnSaved, AbCip browse delay emit, DisposeBridge cancel (review R3)

M1: PageErrorBoundary wraps the body of every InteractiveServer page; the inert layout boundary is removed.
m1: DisposeBridge cancels its CTS when the 5 s wait times out.
m2: a CSV import that commits after the modal closed still raises OnSaved.
m3: document SecurityMode=None no-fallback in Client.CLI.md / Client.UI.md.
m4: browsePageDelayMs written only when loaded or changed; negative flagged.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

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

@@ -3,6 +3,7 @@
 @attribute [Authorize(Policy = AdminUiPolicies.ConfigEditor)]
 @rendermode RenderMode.InteractiveServer
 
+<PageErrorBoundary>
 <div class="d-flex justify-content-between align-items-center mb-3">
     <h4 class="mb-0">Namespaces &middot; <span class="mono">@ClusterId</span></h4>
     <a href="/clusters/@ClusterId/namespaces" class="btn btn-outline-secondary btn-sm">Back</a>
@@ -18,6 +19,7 @@
         <strong>/uns</strong> pages. This editor no longer applies.
     </div>
 </section>
+</PageErrorBoundary>
 
 @code {
     [Parameter] public string ClusterId { get; set; } = "";