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/Dev/ContextMenuDemo.razor

@@ -3,6 +3,7 @@
 @attribute [Authorize(Policy = AdminUiPolicies.AuthenticatedRead)]
 @rendermode InteractiveServer
 
+<PageErrorBoundary>
 <PageTitle>ContextMenu demo</PageTitle>
 
 <h1>ContextMenu demo</h1>
@@ -19,6 +20,7 @@
 </div>
 
 <p>Last action: <strong>@_lastAction</strong></p>
+</PageErrorBoundary>
 
 @code {
     private string _lastAction = "(none)";