feat(adminui): F15 Phase A — shell + auth + fleet + hosts pages

Implements Phase A of the F15 rebuild plan: minimum-viable Admin surface
with a working sign-in path and a fleet-state landing page. Decisions Q1–Q5
of docs/v2/AdminUI-rebuild-plan.md were taken as recommended.

- App.razor (moved into AdminUI library from the Host stub; vendored
  Bootstrap from RCL wwwroot — no public CDN, air-gap safe)
- Routes.razor (AuthorizeRouteView enforces page-level [Authorize])
- RedirectToLogin.razor (preserves returnUrl through the auth hop)
- Login.razor (static SSR, posts to /auth/login; Q5 wording about
  generic-vs-specific LDAP errors)
- Account.razor (identity + fleet roles + raw LDAP groups; Q4 — no
  per-cluster grants; fleet-wide LDAP-group → role mapping only)
- Fleet.razor (per-node deployment status: reads NodeDeploymentState
  + unions with IClusterRoleInfo.MembersWithRole("driver") so freshly-
  joined nodes appear as "waiting"; 10s auto-refresh)
- Hosts.razor (Akka cluster topology: members, status, roles, role-
  leader; 5s auto-refresh)

Host's stub App.razor deleted; Program.cs now points at
AdminUI.Components.App via an added using.

All 104 v2 tests remain green.

src/Server/ZB.MOM.WW.OtOpcUa.Host/Program.cs

@@ -2,6 +2,7 @@ using Akka.Hosting;
 using Serilog;
 using ZB.MOM.WW.OtOpcUa.AdminUI;
 using ZB.MOM.WW.OtOpcUa.AdminUI.Clients;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Components;
 using ZB.MOM.WW.OtOpcUa.AdminUI.Hubs;
 using ZB.MOM.WW.OtOpcUa.Cluster;
 using ZB.MOM.WW.OtOpcUa.Configuration;