fix(adminui): make /admin/secrets interactive - wrap the Secrets.Ui page with a render mode (#483)

The Secrets.Ui RCL's routable page was routed directly, but this host's
router is deliberately static (cookie SignInAsync needs SSR) with per-page
@rendermode opt-in - a directive the RCL page cannot carry, because the
other three family hosts render it under a globally interactive router
where a nested render mode throws. Routing straight to the RCL page
therefore rendered /admin/secrets with no circuit: it displayed, but every
@onclick was silently dead.

Fix: a host-side wrapper page (Pages/SecretsAdmin.razor) now owns
/admin/secrets, carries the standard per-page InteractiveServer render
mode, re-states the RCL page's own authorization policy (the router only
enforces [Authorize] on the routed component, which is now the wrapper),
and renders the RCL page as an ordinary child. The RCL assembly is
de-registered from both AdditionalAssemblies sites (router + endpoint) so
the route is unambiguous.

Guards: SecretsPageWiringTests pins the render mode (the #483 regression),
route parity with the RCL page, and policy parity; the page census in
PageAuthorizationGuardTests classifies the new page and admits the
secrets:manage policy. AdminUI.Tests 665/665.

Live-verified on the rebuilt docker-dev rig with Playwright: /_blazor
circuit negotiated on /admin/secrets and Add secret opens the editor
(before the fix: zero interactive markers, no circuit, dead click).

Closes #483.

Claude-Session: https://claude.ai/code/session_01BL2Vu1ESDQ9SCN4gVKkdts

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

@@ -0,0 +1,20 @@
+@page "/admin/secrets"
+@attribute [Authorize(Policy = ZB.MOM.WW.Secrets.Ui.SecretsAuthorization.ManagePolicy)]
+@rendermode RenderMode.InteractiveServer
+@using ZB.MOM.WW.Secrets.Ui
+
+@* Host-side wrapper for the ZB.MOM.WW.Secrets.Ui secrets page (lmxopcua#483).
+
+   This host's <Routes/> is deliberately static (cookie SignInAsync needs SSR), so every
+   interactive page opts in per-page with @rendermode — a directive the RCL's own routable
+   SecretsPage cannot carry, because the other three family hosts render it under a globally
+   interactive router where a nested render mode throws. Routing straight to the RCL page
+   therefore produced a statically-rendered, dead page here: no circuit, @onclick inert.
+
+   So this wrapper owns the /admin/secrets route in THIS host (the RCL assembly is no longer
+   passed to either AdditionalAssemblies registration — doing both would make the route
+   ambiguous), carries the standard per-page render mode, re-states the RCL page's own
+   authorization policy (the router only enforces [Authorize] on the routed page itself,
+   which is now this one), and renders the RCL page as an ordinary child component. *@
+
+<SecretsPage />