fix(admin): enforce authentication on all Admin UI routes (Admin-001/002)

Admin-001: Routes.razor used a plain RouteView, so the page-level
[Authorize] attributes on 11 pages were inert — every page, including
mutating ones, was reachable fully unauthenticated.
Admin-002: several pages (e.g. NewCluster, which writes config rows)
carried no auth attribute at all.

- Routes.razor: RouteView → AuthorizeRouteView with NotAuthorized /
  Authorizing slots; add RedirectToLogin component.
- Program.cs: SetFallbackPolicy(RequireAuthenticatedUser) — secure by
  default for new pages/endpoints.
- Login.razor: [AllowAnonymous] so login stays reachable; login page,
  /auth/* endpoints and static assets remain anonymous.
- Add [Authorize] to the previously un-gated pages; NewCluster gated to
  the CanPublish (FleetAdmin) policy.

Regression tests in PageAuthorizationTests pin that anonymous requests
to protected/mutating routes are rejected and that login + static
assets stay anonymously reachable. Admin test suite: 210/210 pass.

Resolves code-review findings Admin-001 and Admin-002 (Critical).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Server/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Drivers/FocasDetail.razor

@@ -1,4 +1,5 @@
 @page "/drivers/focas/{InstanceId}"
+@attribute [Microsoft.AspNetCore.Authorization.Authorize]
 @using ZB.MOM.WW.OtOpcUa.Admin.Services
 @inject FocasDriverDetailService DetailSvc